<human>: So here goes my story. Thanks in advance for reading through. 
So my SO and I have had some rough times but nothing like this. We are both in college at the same school where we met and last summer I went away for a medical program for 6 weeks. In that time we had a lot of fights and you can say we weren't really together. I was still completely committed to her though in my heart and mind and I assumed she was too. I figured when I came back we could work on things in person, but attempting to do so long distance was pointless. 
Well. I was right. I came back and we started to talk things out and hang out again and everything turned out great. Except I found out that she slept with someone during that time when I was away from home who had the same name as me who she hasn't talked to since high school. That really... Affected me. 
I'm not supporting a double standard or being misogynistic or anything. Ignore my age because I'm very emotionally and intellectually mature. But I just cant understand how she could do that. She claimed to still love me and we always said how we would always come back to each other. But if that's true, why would she have sex with someone on a whim like that?! She said it was him and her and her friend watching a movie and "it just happened." This was like 2 weeks after I left. 
I don't know what I'm looking for. I guess you can't say she cheated but to me she did. Either way it just really hurts and when I'm with her now I feel happy but the thought keeps coming up and it's definitely affecting us. I just need some advice on how to deal with this. Will things ever go back to normal? Will I ever be able to look at her with respect and love again? Or will I always see her I'm this lust-like way where she can't go without sex for more than a month?

Can you succinctly summarize the text in 1-3 sentences?
<bot>: ex had sex with another guy during a "break" but didn't tell me until after we were back together. Now I'm hurt and need help.