I don't quite know what's wrong

I don't quite know why I feel how I do but I just need to know if any one else feels this way . I have been with my boyfriend nearly two years now when we first net everything was wonderful . It was only when I started to call him on my breaks at work that he used today am just at my friends house etc . I once questioned him about this friend who turned out to be his ex girlfriend from when he was 17 he was 20 at this point. He used to say he was seeing her mum who sis have m.s and I know he did get on well with but it did hurt me so much as I have never been a secure person I was honest and he stopped going round and hasn't ever been since. I am so scared if going to parties etc invade she is there she said hi once at a christening and that just totally ruint my day I just wanted to go home and did as soon as we could . I don't know how I can get over this. Me and my partner had a little boy in October which made me feel horrid for 9 months as I didn't feel me and afterwards I was cold againest him after I had a painful birth and was scared of having sex and being close . This new year we have got back to being how we once was again. Last night we went for a few drinks and was talking about this girl he said he never loved her and made a mistake being with her ESP as she is the local slag bt it's like all our friends always talk about her when they come and talk like my partner is interested in what she is up too . He says she had loads of problems and he always tried to help her. Last night he also said he lived with her for 10 months which I never knew . I just feel like am never quite good enough for him he always used to compare how much he got messed about by his exs and how he worries I could do that I can't get all this out my head and it's making me feel rubbish I really don't know why I see pictures of her and always wonder if he would rather go back to her it's really getting me down now