1st- getting full custody is ALWAYS on the table. BM could die in an accident tomorrow. There could also be 100 other reasons why this child could come to live with his father full time. 

If you cant accept that as an option, you should move on. It's not fair to either of you to be in a relationship where you feel like this. I am not saying that you should feel any other way. Step- motherhood is so often thrust on women an we are just expected to be instamom- but not everyone can or wants to. That is ok as long as you are honest with yourself and your partner. 

You are not selfish, you are smart enough to know what will work for you and what won't. Right now, it won't work for you to be involved with a man who has a child and a difficult ex. There is nothing wrong with feeling that way. Read around this board, there are many women who would not choose the life they now have if they had it to do over again.

Just be honest with your boyfriend. Tell him this is not what you want out of life and you are not cut out to deal with his child and ex. It does not mean you are bad or deficient in some way, it just means this lifestyle is not for you.

The reason you are uncomfortable is you have unequal baggage. Unless he is exceptionately hot, makes a ton of $, or some other redeeming quality, you are the better catch as you don't come with the kid and batshit crazy BM.  Don't beat yourself up - it's just your subconscious telling you the universe would be out of balance. Find a guy in your same situation and build a life together.

Don't waste 3 more years when you know how you feel. Breaking up is never easy but just tell him the relationship isn't working for you anymore or just be honest and say  that you no longer want to be tied to a situation where it's someone else, their kid and their ex having so much impact on your life. I feel if people were honest its be better and open up some of these bip parents to just how shit tu the situation is for the other person. Say that you are .moving out/or he is depending on your set up. Make a plan to move forward and do it. It will never get better. The thing with these situations is that its not just the kid and dadm it's the ex wife too. So really. It is dating all of them. If you're this resentful now, it will only increase over time. And. Dont date a man with kids again. It is so shit for the person who diesnt have any. 

You are not a bad person just because you know what you don't want. I've always known that I didn't want kids. People can think I'm selfish all they want, at least I didn't have kids, anyway, only to neglect or abuse them.

Being a step mom is not necessarily a joy but it's down right stressful and depressing when a high conflict BM is involved. If it's not the life you want, it's not the life you want.

Look, no matter the reason for a break up, the one being broken up with is going to feel it was a selfish reason!

Women get too wrapped up in not wanting people to dislike them.  We are programmed to want people to "LIKE" us.

Look,  if you break up.. it almost doesn't matter why.. he likely won't have the same positive feelings for you afterward.

Instead of being so worried whether he will hate you for being selfish.. cut yourself some slack.  Being a parent (or partner to a parent) of a child that is not yours is no walk in the park.  High Conflict Exes?  makes it even harder.

If you really can't get through to a place where this is an acceptable life for you.. the best thing is to move on for everyone involved.

I'm starting premarital counseling so I can decide if I really want to take on the stress of my fiance's kid and his narcissist ex.  Is this an option?

You have a chance to leave and start over with someone who doesn't have kids. Blended families aren't for everyone. In fact, I would argue they aren't for most. It's an unnatural situation.

Don't feel guilty. You are doing everyone a favor if you make a good decision that will benefit everyone in the long run.

I'm not cut out for the whole blended family thing.......it takes a certain type of person to do that. 

Awareness and acknowledgement of this is POWER!!! Do not deny your feelings on this. This step life is not for you so the next step is figuring out what you are going to do about it....

Follow your gut. That is the voice that is saying--I don't want to live like this. So, PLEASE dont continue living this way.

You control your destiny, no one else. It is ok to say "its me NOT you and I wish you the very best"

Go live your life, your way, on your terms,  abundantly as you can.

sense and wisdom to realize this is not your thing.

3 years may seem like a long time, and I"m sure there have been good times, and fun intermingled throughout. Will those sustain you if you decide to hang in there for the long haul? I think you already know the answer.

Please listen to what your head and your  heart are telling you. When your head and your heart are in the same place, agreement, that is affirmation. Start making plans to  move forward. This is not your weight to carry. You are not ATLAS. You only get one shot at this life, make it great!

I am happy for you.  Happy that you are commiting to yourself to live a great life and to not saddle yourself with tragically flawed people any longer.

Good luck. Enjoy starting  your new life adventure.