Step children need "permission" from their BM to have a relationship with your fiance. (As per Wednesday Martin's theories in the book "Step Monster" 

For sure, considering the way in which your relationship with your fiance began ie as an extramarital affair, BM is not going to give this, because I imagine she harbours a lot of resentment towards you and almost certainly blames your fiance for breaking up her marriage, although she should blame you.  

I got the same treatment from NPD BM, and my relationship with my DH didn't start until he had moved out of the marital home, so there was no question of me "luring him away".  

The best thing you can do is give your bios a bit of time, but leave them in no doubt that you and your fiance now come as a pair, and that you will expect them to eventually meet her, and what is more treat her with courtesy and respect.  You could point out to them that any anger they have about the way you split with your ExW should be directed at YOU, not at your fiance. 

Do not get into the habit of seeing them without taking her along, this is disrespecting her.  Make sure your bios know this, and that you will not tolerate any discourtesy towards her.  

My ex (The Ostrich) did the same thing before he met me- his wife would tell him that his kids hated him for leaving their BM for her. I then began to feel their dislike and possible hatred for me after I met him. These relationships are incredbly complicated but here is my take on what should happen:

Let SM free to make her own choices about whether she spends time with them-I felt co-erced into being involved with theskids when I wasn't ready- and eventually came to resent this. My feelings, when expressed openly and honestly, were not treated with respect. So, value SMs feelings and listen to her- give her time.

Don't let her give them any money- they are adults, and will see this as buying their affection. The Ostrich was always over generous with my kids and they didn't need it or appreciate it. I was the parent and the choice over how much to support them was always mine.

Think carefully about how complex these relationships become, the slightest mistake, remark, even the way they look at each other, will be picked on and dissected by both parties.

Lay down some ground rules on both sides, particularly when it comes to the wedding. Be prepared for game playing on behalf of the kids,who will be reporting back to BM on everything.

In the end you cannot control the behaviour of these adults- you ar ein for a bumpy ride over the next few months.  Give your SO and your sons all the space you need.

And please, please,please don't be an Ostrich. I think it is wonderful that you have come here and sought advise, let us know how you get on.

Listen to your SO, don't force anything, and treat your sons like the adults they are- don't accept any childish or immature behaviour which BM may also promote. Be strong, be fair and listen!

"Blah-blah, blah i'm a good guy."  You lost me on the first few paragraphs.  You really might be a great guy, but if you present yourself as you offer here to complete stangers? Yay, I'd respect your children's feelings & desire to have jack-sh*t to do with you, too.  Kids may have made a good choice.

Woosing out & hiding behind a girlfriend's skirts? "My kids are mean to my GF, what do I do?" (Wailing violin)

You have found a deep love & wish to create a new life for yourself. Let your kids go. They are more or less adults. No blame. They will circle back or not. Acknowledge that you have moved onto a new phase of your life. 

Don't force an artificial caring, fantastical relationship. Like trying to force panty hose & a girdle on in Houston ... in the summer.  Aim for polite, distant courtesy. Air-conditioned family. Christmas cards & wedding visits. Relax

Both you and your SO need to be very careful what you wish for.  Trying to develop a relationship with these two young men may be fraught with pain.

Here's the advice I would give your fiance, so please read it to her: 

Don't push any kind of relationship with these two boys.  It will never work.  NEVER. As others have noted, the BM is the lynch-pin here and she will always ensure her sons have her back and are loyal to her. 

No matter how "nice and polite" you might get them to act in front of you, there is always danger hidden in calm, deep water. Every time they visit or meet with you, the BM will undoubtedly pump them for information about you and will find ways to get her digs in - overtly or subtly.  And if you think it's bad with the SS then just wait until they marry and grandskids come along!

Face facts:  These two young men will never want a relationship with you.  They love their mother and are already convinced on a cellular level that you harmed her.  No matter what their father tells them, mother-love is stronger and they will never believe him. This will never change, no matter how much time goes by.  If you are hurt now by them ignoring you, imagine the hurt they will cause you if they feign liking you and then find ways to stab you in the back. 

Keep your purse closed, too.  Nothing you do or buy for them will work.  It is money wasted and if they knew you were providing it, they would be laughing behind their backs about it.   

No amount of patience, attention nor money will bring these two around to your corner.  Accept that now.  Go on and enjoy your marriage and let your DH keep his sons to himself.  

Take it from someone who has been in this game for almost 14 years.   Don't bother trying to incorporate these SS in your life.  It will bring you nothing but disappointment and heartbreak.   If and when you ever meet, be cordial and polite as you would to any stranger.   Because that's all they will ever be to you. 

Okay, let me get this clear.  You thru a hand grenade in your family and now that the damage is done you want to know what you can do to fix it without any condemnation on you for throwing the bomb?  Sigh, I guess we don't have to as your kids have already done that for us. 

First, go to exetiquette.com and figure out how to co parent with your ex.  Your kids are still pretty young and they have already been thru a lot.  Don't tell me you don't want to do it.  Don't tell me bio mom is unreasonable.  Find neutral ground with their mom.  Put some time and effort into it. This will be the first step to STOP putting your kids in the middle of your relationship. This is key to telling your kids that they matter to you.

Second, man up to your kids and tell them you are responsible for the affair and that it is 110% your fault.  You chased her, you lied to their mom, you did the deed, and when given the opportunity to salvage the marriage you said No Thanks and moved on.  YOU DID IT.  Right now, you are thinking that an appology is enough but when your kids reject the OW (other woman) what I hear is that the kids have not given up on the blame game but they have moved the responsiblity on to her instead of confronting you.  Most kids do this, in fact a lot of adults do it too.  If you want to ever have a chance of them at least tolerating her then you have to force the kids to move the blame back on to you.  Hard to do since it means putting yourself in the line of fire and staying there.  It will be painful.  It might take years.  It is not an appology, or sucking up to them, or trying to win their forgiveness.  It is a brutal, fearless inventory of your fault that you share with them openly.  Only when your kids see,over time, that you are serious about owing this will they consider letting your fiance off the hook for the affair.

Last but not least - quit calling her their step mom.  She is NOT there SM and she might never be their SM.  At best, you might hope for them to call her "their Dad's wife" but SM is offensive to your kids.  Trust me, you would be appalled by what they call her behind your back right now.  Dad's wife is a giant immprovement. 

Your sons are adults.  You have apologized to them and explained your side of the story.  It will do absolutely no good to continue to try and convince them of your situation and how you feel.  They are a different generation, therefore, are on a different page at their age.  

Moving forward from this day is the best you can do.  You are going to move forward anyway.  If you continue to "beat a dead horse to death", it only stresses your new relationship as well as your relationship with your sons.  Treat them with respect, treat them like the adults they are, and let them make their own decisions.  You are feeling guilty, that is obvious.  

The best advice you can give your kids, is example of how you live.  They learn by example; it's like seeing inside beauty.

I have been in this SM position and almost identical situation for 38 years.  My SD57 has never recovered because her Dad introduced me to her, before BM and his divorce was final.  When I met DH, he was living out of his own home and going through his divorce.  The divorce was a long process, because of property settlement.  I was also going through a long divorce for the same reasons.  I have never known BM and my DH has never known my Ex; therefore it had nothing to do with an affair.  But my SD57 has always looked at me as the "other woman" and in the same breath says her "Mom is a nut case".  I have never responded to my SD's behavior toward me, I have tried to set an example by keeping my mouth shut, hoping she would do the same someday; it hasn't happened yet, but I'm over it and have my own life with my DH.  My two adult SS's are very respectful to me.

You won't win this chase game, so make the best of it.  Please do one thing, stand by your woman and demand the same respect from your sons for yourself and this new woman in your life, that you will show to your sons.  That is all you can do.  

Advice for your fiance', do not force yourself on these young men, do not lend them money, do not get involved with the past, and concentrate on building your relationship with their father.  I would not lend any of my family, nor DH's family, money; it causes lots of problems.  Let BM give them money, she has obviously influenced their opinion of you, so she can pay.  :)  Be a nice person and move forward without the drama.

Good Luck Stevedr

Steve, I'd treat your kids and fiance just as I would if introducing two cats or new chickens into a coop; use caution and you may need to keep everyone apart for awhile.  Parallel relationships will have to take place until your kids can heal from the shock of their family falling apart and to be honest this may be indefinite.  

The actual wedding is going to be a huge issue for your sons and they likely will refuse to attend since in their minds it may betray their mother in some way.  I'd seriously consider *eloping*, just you and the misses to some fantastic venue.  I'd skip a reception altogether since it will only be another triggering event, unless of course it's important to your fiance then go all out. Just be aware that your sons will likely shun any event that signifies union w/you and someone who is not their mother.  

Best of luck, you're gonna need it!