<human>: Can you give me the gist of the text in a nutshell?

So I'm hurting pretty damn bad.

She and I, along with a group of our friends(group 1), and a group of one of our friends friends(group 2), went on vacation together for Spring Break. A week before we went, I told her that I was in love with her and (understandably) she didn't reciprocate at the time.

So the vacation goes on without a hitch, we have a small arguement on our third night there about her unintentionally flirting with one of the members of group 2, and we made up the same night. Our final night there, since I was the one driving everyone home, I climbed into bed early while everyone else continued drinking.

While I was away the guy from group 2 and her made out with one another, and I wasn't made aware of this until we made it back home from vacation. So we broke up.

She's now talking to this guy on a serious level and I really, really want to be happy for her, since she's happier, but I can't bring myself to do so. 

A few side notes:  
1) The same night, the guy from group 2 also made out with her older sister and tried to have sex with her (the sister) while she was in the bathroom puking and crying.  
2) We are neighbors, and all of our friends are mutual. (I see her everyday, in my apartment.)  
3) Everytime I see her I just want to express my feelings for her and let her know that I am still deeply in love with her.
<bot>: Girlfriend, now ex, cheated on me. Is talking to the dude she cheated on me with. She is neighbor.