1.  It's really difficult to manage when people aren't sticking to a preset custody schedule.  Reasonable shifts to accomodate very special events not withstanding.

2.  You should by all means NOT do any thing that is intended to forge any bond with your SO's EX.  She does not want you to send the kids home with arts and crafts projects..  enjoy the kids to the extent they enjoy doing things with you in your home.. and leave it at that.. don't send trophies to his ex

3.  Your SO had kids with her.. so he gets to deal with her objections in your home.. HE is the parent.. and I don't care whether it was you that suggested the film they saw.. as their FATHER.. it was up to him to allow or not allow and decide what was appropriate.. and it is up to HIM to tell his EX to stuff it when she tries to control what happens in his home.

Don't take out your frustrations with her attempt to control your home on the kids.. but neither should you overly go into MOTY (mother of the year) territory with them... be pleasant.. and support your husband having his children for visitation.. but I would not be playing a huge mother role with them.. but sure you can do fun things with them if they like it..

but be mindful that doing "too much" can be viewed as trying to one up their mom.. and you can expect some fallout for that.. it may mean you do less.. and that's kind of sad.. but we all deserve a drama free life.

Welcome!  Your BM is a very controlling person and your BF is afraid of rocking the boat, afraid of her and fears losing contact with the boys.  It isn't even good for the kids.

Does he have a CO?  Bottom line, you have a BF problem.  You're not wrong and your reactions are normal.  Nothing will change til he sees the light and puts down sound boundaries (no controlling what they do on his time, limited contact with her based only on a few topics, scheduled visitation with no deviation, etc).  Frankly, many of these men dont have the guts or intelligence to implement these boundaries.  I'd hate to think what his finances are like, tell me he's only paying the court-ordeted CS.

Good luck, you sound like a thoughtful and caring person.

Flexibility is great. It's great for the one who makes the decisions, anyway. With your bio-kids, you (and your ex) do, so it's great for you. With your SO's kids, his ex makes the decisions so it's great for her. To me, unless all parents and stepparents have equal say in the flexibility of the schedule and get along great, the best thing is to have, well, a schedule. One that doesn't usually change unless it's something important. Everybody knows where they are sleeping on any given night and they have the ability to make plans based on some reasonable amount of certainty. I would imagine the kids would benefit from some stability, too. 

OK, so a lot to unpack here.

1) your SO has "not done the work." He has left his balls in his ex' purse. There's a saying here on Steptalk. Doing the work means that the split couple has done the work to make the split. They are no longer enmeshed, they have custody/court orders properly outlining the custody schedule. It's hell on earth to live in limbo not ever knowing when a kid can grace the ncp with his presence. Then the ncp parent lives constantly on edge afraid to do anything because their little poopsie might miss out or not want to do it if they show up. 

2) Your SO is allowing his ex to control everything. Your SO has totally abdicated his role and rights as a dad and 50% of the parenting equation. You are not putting him in the middle and don't let him claim that you are. He is because he has lost touch with his nutsack. He's a chickenshit to his ex and he is exhausted because he's constantly dancing to the tune of his ex and his kids. He's likely allowed his kids to have more power than they should as well. I'm curious to know why you're asking if you're being selfish, controlling, etc. If it's your SO trying to tell you that, then he's only trying to get you to stand back like a Stepford wife and eat shit. Be happy with pittance for attention. Don't say a word.

3) Your SO doesn't sound ready for a relationship. He needs to gain control of his divorced dad life. He can't have his cake and eat it to. If he doesn't have time for you because of running around in circles dancing to the tune of his ex and kids, where does that leave you? To get laid at night? To hell with that! He's not able to dad and partner at the same time. You have every right to expect to get your needs met as a partner when you become involved with them and your SO is not meeting those needs. You should not be chastized for having those needs, so if your SO is even hinting at that, he is the one who is unreasonable. He can't expect that he can drag some poor innocent woman into his mess that even he can't handle.

4) In my house, it didn't occur to me to not start my own traditions. You are the woman of your house: not your SO's ex. Take back your power. Start off by planning activities. "The car leaves for the pool and then library and then the pancake house at 4. Whoever is at the car with their swim bag at 4 on the dot is welcome to come." Period. End of story.  "Dinner to meet Aunt Lucy's new boyfriend at 6. Car leaves at 5:45. Be there or be square. Whoever wants to come is welcome, but car leaves at 5:45." So, like that. Whoever wasn't at my car when I was leaving didn't go. 

5) Your SO's ex likely knows how to make it so that the appearance of the boys at your SO's interferes with your SO's time with you. The lengths that HCGUBMs will go is unreal. I wouldn't put it past her to have figured out how to cockblock. And no, it won't get better. She's learned that what she does works. She won't stop until your SO wises up and stands strong in his boundaries or you leave. 

6) No things won't get better. Once a Disneyland Dad, always a DD. The issue that causes a dad to lose his balls is so deeply rooted that when the kids get older, the dad will sabotage any evolvement or maturity as a way to hang on to the kids. He'll deeply regret not having been able to live with them full time while they grew up that he'll desperately make things worse so that they might have to move in with good old Dad. Things will get worse. The toys get more expensive and the SM is the one expected to pick up the pieces and fund any retirement or vacations because the dad forked over too much money to the expensive toys like cars and uni for all of their kids. So, no. Things won't get better. They'll get worse.

Toss this one back. He's not ready. He would need therapy to get to the root of why he has allowed his ex to control his life and rather than get therapy to learn how to stand up to his ex and kids, he'd rather have you believing that you're the one causing him to be caught in the middle. How dare you have needs as a spouse?! So, yeah, toss this guy back. He's not ready. If you're still available when he's done the work to make himself a viable partner, then perhaps he can give you call, but he's not even close to being ready yet.

This is a mess. He can't possibly be ready for a relationship with you because he's still too busy managing the relationship with his ex. Whatever she wants, fine. Whatever you want, he has to check with his ex "for the boys."

Live you life. Make plans with your kids. Don't let HIS (or rather his ex's) plans impact YOUR time with your kids at all. If you plan an activity or a trip, go without him and his. Why should you and yours miss out?

I don't know if she's super controlling or if it crosses the line to abusive, but your SO doesn't seem to be doing anything to untangle himself. Would he consider counseling to sort through this? He needs to learn how to make his current relationshp a priority.

I am very sorry to read what you are going through :(  you have a controlling high conflict bm, and you are right to be fed up. You also have a dh problem in not setting boundaries OR standing up to her... 

She is totally manipulating the fact there's no formal arrangement in place. This is where,  if you get fed up enough you can come to ultimate time with dh.  Court isn't just for abuse its for setting up child arrangement orders, you can even DIY it.

You have to do a mediation meeting first with a registered mediator, set out exactly how you wish contact to run (days/nights you have the children , methods of communication etc) then if you agree both parties sign. If you can't agree you can either go for more mediation , or , you tell the mediator you've had enough and you would like the form for Court. It's that simple and there's a lot of Internet help to DIY it. Failing that you can hire a solicitor or a mcenzie friend to help you.  The best time to do it is now, as when they get to 13/14 it's too late, especially if they've been worked up the back to say what mummy dearest tells them.

She doesn't get to dictate beforehand what skids do during their dads custody time. So if she doesn't ask her exhubby first if he is ok with their extracurricular activities and taking them to it during his weekends, then they spend time with their dad

if biomum kicks a stink, put it back to her if you did the exact same to her, no way would she allow it

You've been given a lot of great perspective here and I scanned most of it so maybe this has already been covered, but just a point on the relationship between you and your SO: you mentioned that you're feeling distant toward him. That's the resentment creeping up, which it will inevitably in this situation because it's so insane. And if you haven't already, you'll also probably lose a lot of respect for him because it's a major turn off to watch a man allow himself be controlled by someone.

Resentment and loss of respect are relationship killers, so I think your only viable option left if you're not ready to leave and he won't make changes to the set-up with the ex are to 'drop the rope' and just live your own life the way you want to while still in the realtionship with him, which I think you said you are already starting to do. Maybe he'll shift accordingly, maybe he won't, but at least YOU won't be letting yourself be controlled by these other people. You don't want to compromise your self respect to be in a relationship.

You don't want to compromise your self respect to be in a relationship.

And great advice has been given! 

I'd add...you mentioned love and compassion....you seem like such a lovely,  sweet, caring person...but direct some of that love and compassion back at yourself!  You are tremendously stressed (been there, so I can recognize it!).  You have sacrificed yourself on the alter to this man and BM and the boys....and honestly you probably already know its not for the boys,  its just what BM has always done (gotten her way) and your SO has settled into doing her will. At least that's how it seems.  Honey, I wish we could go out for drinks and talk!

If your relationship is going to survive and thrive,  some changes are going to have to come.  You are entitled to a life where you determine your own schedule based on an agreement with BM, preferably chiseled in stone via court order or equivalent.  Something that allows you to plan how you spend your child-free days, have date night or sleep in! At your house you get to choose movies and activities while BM is granted the same courtesy at her home.  Activities on your time are not decided by this enmeshed mess of a heifer!

In reality,  if you want to continue,  you will need to help the situation evolve.  Make a decision that your home is just that and you're the activities director when the boys are there. You're perfectly competent to choose movies that are appropriate.  You can also introduce new foods or different ways of eating foods they like (square shaped pizza tastes just like triangle pizza!). 

Preemptively make plans and have SO put BM on notice that you're out of town or whatever for a weekend. 

Definitely lock down your social media so she can't stalk you! It's none of her business what you do or when you do it or who you do it with.  She's gonna have to learn to cope and that's all there is to it. Or she can continue to be miserable,  but don't let her drag you along.

Take yourself out on dates!  Tell him you have some "me time" scheduled for yourself while he does BMs bidding. And let him wonder. Also tell him you'd like some couples time...that he should arrange for BM to keep the boys....definitely keep your head up and keep your options open. SO needs to disentangle himself here and he can, if he's willing to. 

You were not stupid for putting up with it all, you were simply too kind. You wanted to help - that's not being stupid. You've gained clarity.

I'm happy to see that you're chalking this up to experience and lessons learned. I'm also happy that you'll be out before Xmas. This could be your best one yet!