Do you know his family at all? Know anything really about him? I would see if there are other student moms and see if I could join a group of some sort, take as much pressure off yourself as you can.

It doesn't sound like your boyfriend is responding well to being a father/having a girlfried who is a mother. I don't know that you can get back that part of him you enjoyed when you all were first dating.

I would figure out a way to take care of myself and son. Doesn't sound like you'll get much besides "breaking down" from him. Get in a good support position and then confront him to see if he's willing to go to counseling or help more or change in any way. Your weight shouldn't have much to do with anything. It's not like you're lying around doing nothing but eating bon bons! Get support for yourself, however you can. Favorite teacher you can talk to? Your own counseling at school?