Emotionally Unavailable...?

I'm in a "relationship" and have been on and off for about 2.5 years. I love him but am not in love with him. Actually, I am very unattached to him. It's very strange but it's like I don't care if he comes or goes, if we break up or are together...its like every emotion I have for him has died. There are various reasons why I think I may be this way (during our 1st year of dating, he was a very bad boyfriend, don't ask why I put up with it, but I did, hoping for things to get better). I'm not really sure how to help myself "feel" again. I have had several boyfriends in and out of my life after my "first love" but NONE of them I have been able to get attached too. It's like I want the perks of a relationship without the strings attached...I don't plan on cheating but when things get too serious I freak out....but at the same time i WANT a relationship...Why do you think this is happening and how can I help myself? I seem to only hurt those in my life (including "bf"). Advice?