relationship advice..?

ok here goes...sorry!

i am 26 i met my b/f online 2 yrs ago, he started to work down by me so we could see each other more and he stayed alot at my house, things were great, after a yr we got engaged, then i fell pregnant an it kicked off, he was horrid telling me it wasn't his etc etc, we both have children from previous relationships, (although up until recently he didn't c his child) we split up and i lost the baby at 12 weeks, we stayed in touch an after a few months got bk 2gether and things were as normal, our relationship is either really really good or really bad, we go through patches of constant arguing and split up for a few wks then get bk 2gether, this last time was different though, i think he slept with someone else while we were apart as things were different in bed and he doesn't want to commit, he says he loves me and wants to spend the rest of his life with me but doesn't act like it. recently he has been seeing his child again on a regular basis and things have got worse, every week he takes his ex out and their child but refuses to tel her he is in a relationship, she thinks hes single and flirts with him, he says he hates her but puts kisses on the end of some txt msgs and is always really friendly with her on fone. am i being a mug? can this ever work? before we had a future now i just dont know if hes using me until they get back together. none of my family and friends like him because when we row he threatens me and everybody says there is just something about him they dont trust. help