Do you mean fear of commitment? You sound very insecure. It is difficult to relax and trust when you have been hurt before and this is a really normal way to feel. Are you trying to protect yourself in case it all goes wrong again by not getting in too deep?
I have been in a situation where I drove my partner away through excessive demands for reassurance that he loved me and wasn't going to leave. He just couldn't hack it. We have now been married for 8 years, so it can work out OK.
I'm an obsessive, so my methods may not work for everyone!! First, I realised I had to have a "Plan B" in case it all went wrong. I worked out who I could depend upon for emotional support, where I would go, how practical things would work out (money, house etc) It's true that none of this will stop your pain if it goes wrong, but it gave me a bit of a sense of security that wasn't built around my partner.
Secondly, I realised that I had to stop the obsessive questioning. This is hard. Eventually, when I felt a question coming on, I would think to myself "I know what he will say. It will only reassure me for a moment and then I'll start worrying about the questioning again". If necessary, I took myself off to the loo to think it through. The only downside is that people start thinking you are incontinent
Reassure your partner that this is your insecurity and is nothing they are doing wrong. Ask for her support.
Finally, I found a really good, patient friend whom I could drone on at instead of my partner!!! It takes the pressure off the relationship. You could always use this site - you have a problem many of us can relate to. Also, see the thread started by Thinkalot called "Another way of dealing with obsessive thoughts" (or something like that - sorry, too computer illiterate to do links and stuff)