<human>: Could you distill the essence of the text into 1-3 sentences?

I was finally feeling better about our breakup, we have been together a long time but both needed to move on because he was graduating college (I'm not finished yet) and I want to be more independent, but he still wanted to be friends after the breakup. I quickly learned that this meant sex when he wanted it or companionship on his terms if he was lonely, which was terrible and made me feel like a doormat. I didn't really indulge him and am now studying abroad, but I found out a few days ago that he hooked up with a girl he has been friends with a long time only a few days after I left town. Not only that, but this girl is someone who I long suspected he had feelings for during our relationship, and had caught him talking to her late at night on facebook (it was an accident - he didn't want me to see nor did he tell me they would talk so frequently, and at night) last year which destroyed me. He always told me he wasn't interested in her but he obviously got with her the first chance he had and then told me about it. 

I am not upset about the breakup per se but absolutely destroyed that he did this. It seems so cold after he knows how I feel about her, and my confidence is shattered. I can't help but think he thought about her our whole relationship. I have self-esteem issues and compare myself to her, and am so embarrassed to ever see her again. I am still just shocked that he would do this to me. How do I begin to cope with this? I don't think I am being over-sensitive - I have never liked this girl and have always been jealous and he knows this. I don't know if he really doesn't respect me or if he was trying to spite me. This girl is also shady as fuck, and cheated on her boyfriend with some guy I know and is still with this guy, yet she still hooked up with my ex. I don't understand how people could do this. :(
<bot>: My boyfriend hooked up with a girl I have always been jealous of in our relationship and I am horrified. How do I deal with it?