Re: Whats the best outcome here? -need some good advice
Every non-maternal woman that comes into that child's life (of which it appears there will be many, given your description of you and his ex) will screw him up more and more.
Don't say you don't know what it's like to be a kid; you were one not too long ago. Perhaps you need to analyze why someone who doesn't want kids would move in with a father (...who, coincidentally, is attracted to non-maternal women!) Certainly you can see the issues here are more than surface.
"It just makes me mad..." "It's not my fault.." "He pressured ME..." etc, etc indicate you are just not ready to be in a serious relationship, much less sign a lease and take on a child.
"My happiness matters too" Not at the expense of an innocent child's mental health. You're supposed to be the adult here, but you make it sound like your bf has TWO children to raise with all the whining about "Me, me, me". It's exactly this sort of attitude that causes bad parents to keep on reproducing children they are incapable of parenting, and extending the cycle. Perhaps bf is one of them, if he cares so little about his son he would accept a woman that barely tolerates his child!
You want to be "happy", fine, but having these responsibilities are too much for you now.