Self-Destructive Behaviour - ruined the best thing in my life

Hello everyone. This is my first post here. My story goes like this: I was always very emotionally vulnerable and naive. I always wanted to believe the best about people. When I was 16 I was raped by my boyfriend. At the time I didn't understand that it was rape - it wasn't a stranger in a dark alley, or drugs in my drink. I said no, but he just did it anyway, and for a long time I didn't understand why I felt so bad about it. You're meant to enjoy sex with your boyfriend, right? Anyway, the relationship grew more and more abusive. If I tried to leave him he would lock me in his room or pin me down. He controlled what I wore, where I went, everything.

I finally escaped when I went to university. He couldn't get me there, so I broke up with him over the phone. I felt so free. But by the end of second year I had developed depression and bulimia. Food was all I thought about. I would secretly binge, then make myself sick, then cry until I went to sleep. I got help, and my doctor put me on anti-depressants. It helped a bit.

I also started sleeping around a lot, sometimes 3 or 4 different guys in a week. Looking back, it was probably because I felt like sex was the only thing I was good for, and my self esteem was so low that if anyone wanted me - even just for one night - it felt good.

Slowly I overcame my depression, however, and began to value myself again. It was then, after getting my degree and starting my masters, that I reconnected with an old school friend and fell in love. He is wonderful, intelligent, and gloriously weird, and most of all, knows how to keep me calm and make me happy.

So what do I do? I cheat on him. I slept with someone. Terrified, I tried to tell him. I said I'd cheated on him, that I'd kissed someone. He asked if it had gone any further, and I just said no. I was so scared of losing him, and his forgiveness felt like something I could never hope to ask for, that I couldn't bring myself to tell him the whole truth, which is as bad as a lie. He forgave me for the kiss, but still doesn't know the whole truth, and it haunts me every second I'm awake, and sometimes in my dreams too. I don't know whether to tell him everything, which would destroy him, or just vow to never let it happen again and move on.

So I now feel like I am back at my lowest, constantly doubting myself and fearing the worst. I want to be strong, but sometimes I feel like the only thing stopping me from hurting myself is knowing that it would hurt him. My old eating habits are also creeping back. I'm alternating between 'you don't deserve to eat, you should starve' and eating so much I am sick.