It sounds like you guys are just doing things out of order. This is not a criticism. I don't know details about the timing, but it seems that you didn't work out certain important issues before adding the strain of an unexpected pregnancy and then child to tend to--how you fit into his life with his ex and their child, giving them a chance to get used to the idea; his mother getting to know you and learning to like you with her son. (Maybe she saw him make poor decisions before you and had no reason to see you as a good decision. Family doesn't tend to share that kind of information with the newbie; they just keep their distance until they see that it's real.) These are just two big issues that can put a huge strain on any relationship. While you don't HAVE TO wait, it's wise to do more planning (for and against certain things) and consider the timing, if you want transitions to be a little smoother. Otherwise, you're just piling on everything at once and expecting everyone involved to just take it. You want people to feel the way that you think they should about it when you have not allowed them time or opportunity to process it like they need to in order to come to their conclusions. If you sit down to a huge steak and potato meal and finish it in three minutes, chances are that you will be feeling very sick and possibly throwing it back up. There's wisdom in taking bites and chewing and letting it go down bit my bit and then letting it digest. Some things can't wait, but....
With that said, it sounds like now things are settling into place for him and he is in a better position to pick this relationship back up and move forward with you. If you think that you want to be with him, see a counselor and acknowledge and discuss what went wrong from each perspective without judgment. Use counseling as a tool to understand who each other is, who you are, and what works for you.
It is quite possible that things are smoother with his mother and with his ex because a little time and effort have been applied to the situation. Thsi might be why he is now willing to try again. You shouldn't expect things to just fall into place and bend to you because you are "in love".