I'm sorry about what is happening to you, I think you should leave him.
To me it seems like he is using you, and doesn't appreciate the things you do for him, he doesn't deserve forgiveness, any man who cheats on his wife 2 weeks after his child was born is screwed up in the head.

He should be lucky to have you yet he does this to you, I think your child deserves better then a user for a father.