I don't get it...should I just give up on my ex?

my ex and I broke up in July of 2008. we have a child together that was born only a month and a half before we broke up. the reason we broke up was because he said I was unstable and extremely jealous, and I said I just couldn't stand him talking to pretty girls (I felt ugly because I just had a baby so what guy would find that attractive when they have beautiful friends? I mean, at the time I thought why would he wanna be faithful to me? I had some stretch marks and a fat stomach because I just had a baby...why be faithful to a fat cow when you can bang a skinny girl?)

we never stopped seeing each other though, we started talking a few days after we broke up and he would come see our daughter every day. he still comes over almost every day but now he has custody of our little girl because the courts said a person who is bi polar should not have a child alone, that people with mental illnesses are not able to care for children. I see her a lot and he comes over and we go out.

but he won't get back with me, he says he loves me but he said he doesn't like the way I'm so insecure and destroy myself...i honestly think it's because I'm not skinny. I wanna be thin again so bad but I'm having so much trouble losing weight. I'm not fat but I'm not model skinny like I have to be in my crazy head. all his friends have skinny beautiful girlfriends so in my bipolar brain I think "he doesn't wanna be with me because I'm not as pretty as them...he would be with me in a second if I was skinny" but he says what I'm thinking is crazy person thoughts and I need medicine and to shut up and stop being crazy

i also asked him if he is just loving me and having sex with me til he finds a skinner prettier girl he said no he has no intention on finding someone else...then why would he wanna be with only me but not be boyfriend and girlfriend? I don't get it...should I just suck it all up and tell him I'm over it all and ditch him and just deal with all the heart ache and probably get on meds so I don't do something to myself? or should I just stay with him even though we aren't boyfriend and girlfriend and only be with each other and just get real thin and see if he still feels the same way?
I don't get it...should I just give up on my ex?
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