How do i cope with the pain caused by him?

Where to begin? About 5 months ago my boyfriend decided that we should break up. He was living with his family and we both were very unhappy. I ended up moving 150 miles away to my hometown. Soon there after we had broken up he began dating this, how should i put it in nice words?, a umm lowdown tramp. This girl was the most promiscuous girl that I had ever met. Anyways, they hooked up, but he couldn't stay away from me. We would text nonstop and he would come and visit me every few weeks and most of the time we ended up having . I told him I would only permit such acts if he wasn't having any ual contact with her; which he convinced me to believe he wasn't. Soon after we broke up I ended up heartbroken and lost myself in another mans arms one time. I regretted it terribly though, but I kept it my own little secret. I felt that my boyfriend (ex at the time) was having with that girl, but I really had no proof. I figured if he kept his secret, I would keep mine. We ended up getting back together and just got an apartment together. Just the other day he let me use his cell phone while he was away on a job so I could call his work phone. Low and behold were texts that he had sent to his skanky girlfriend. They were very in depth texts about the ual things he wanted to do to her. They engraved an image in my head and a scar on my heart forever. However he denied these texts, saying that his friend probably sent them while they were drunk. Finally after drilling him about it for 2 days and admitting my little secret he came clean. He was admitting all the things he lied to me about. Now the images of him and her are stuck in my mind. They're all I think about everytime he touches me or kisses me. How am I supposed to cope with all these lies he told? He's talking about moving on and starting our relationship over again. He's talking about marriage,