Having problems dealing with feelings about my ex fiancee

My fiancee and I broke up 18 months ago, not because we didn't love each other any more but just because we didn't think it was working. It was hard and heartbreaking and every second of every day I just wanted to try again. I decided to get into another relationship to try and move on with my life, and he dealt with things in his own way, generally being with his friends and throwing himself into his hobbies, I guess everyone deals with things differently. We had a house together and stayed living together as neither of us could afford to move out, and we actually carried on getting on really well and started to get even closer than we were, which I didn't think was possible. We had to move out of our house about a year after we broke up and we decided to get a new place together. Everyone thought we were mad but somehow it worked for us, and we were both happy as we could stay together as neither of us could quite imagine not having the other in our lives.

I carried on with my new relationship, got promoted at work, carried on with my usual social life, and my ex did the same, often socialising together with friends. I often said to my friends that he is the only person I can ever see myself settling down with and that he is, and always will be, the love of my life. I always said that we never broke up because we didn't love each other, just that it wasn't the right time, and one day we may be together again. My new boyfriend (who I have since broken up with) was a great guy and we had fun, but he wasn't going to be long-term and would never be my ex, so I eventually decided to end it as it wasn't going anywhere.

One night about two months ago I got drunk one night and told my ex I still loved him and thought constantly about being back with him and wished that we had never broken up. He said that he felt the same and would always love me more than anything and nobody would ever compare to me, but he was scared to try again in case it didn't work as the pain he said he felt when it ended was the worst he had ever experienced, and then he would lose me as a friend too. We have been going backwards and forwards with this for weeks now, he treats me like a girlfriend most of the time but seems too frightened to take that actual decision to be with me again. I get so confused as surely if he loved me that much he would want to take the risk and be with me as couldn't live the rest of his life wondering what if, as I know I can't do that and it is driving me insane that I may have to? And he says he can never love anyone else but me, so why does he keep taking a step back everytime we get close to something?

I also found out a few months after we broke up he had a one night stand with a girl he met in a club, he doesn't even know her name or how old she was, and left the next morning without even getting her number. He said it was the worst, most horrible experience of his life, and he would never ever do it again for anything in the world, and he was disguisted with himself for stooping so low and doing something like that, but it just happened and he said he knew all along it was wrong and he was going to regret it, but he just did it anyway. We started going out when we were 24, I was his first girlfriend, first love and first (and only until now) sexual partner. He is a very good looking and popular guy, we were friends for a year before we went out and girls used to throw themselves at him on nights out but he always turned them down, as said he didn't do things like that and there was no point being with someone unless it was going to lead to something special and long-term and that he was saving himself for the right person. So when we got together it was the best moment ever as I knew that I must be so special to him and that he thought a lot of me. He always gave me faith in men, that they weren't all the same and that there were some good ones out there, and a lot of the reason I trusted him so much was because not only did he love me and not want to cheat on me but he wasn't physically or emotionally capable of it. Now to find out he has done something like this has broken my heart and made me question everything, I feel like I just don't know him like I thought I did and I feel uncomfortable and unsettled in my own world now as everything seems so wrong. I am not mad at him as he is single and can do whatever he likes with his time, I am just upset that everything I believed about him isn't quite right, and now my emotions are all over the place and I keep having nightmares about him being with this girl. He said she is absolutely nothing compared to me, and that it was a huge mistake and he is so angry at himself, and I believe him, but it is the fact that he could do something like that to start with after everything he has said and believed in.

I have suffered for most of my adult life with severe body image problems, and hate how I look and think everyone is prettier and better than me. Everyone I know says I am pretty and have a figure to die for, and I have men queuing up to ask me on dates, and have even been offered modelling work, but I just can't see it, so of course I now think that this girl was prettier and sexier and he wouldn't even think about coming back to me now (although my best friend did point out that I am the one beating off eligible men with a stick whereas she had to make do with someone who wouldn't even give her his name!) and it is all getting too much for me.

I am so upset and confused and hurt at the moment and have no idea how to move forward or cope with things.