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

My girlfriend had cheated on me right before finals with her ex boyfriend. It absolutely devestated me, and didn't make taking my four finals any better. I decided to give her a second chance a few days ago, but then I found out she was still having sex with her ex boyfriend. Literally last weekend. She keeps saying that what is going on between them has nothing to do with me and her, at this point I think she's out of her mind. I just wanted some advice on how to get over her. To be honest she was a great girl and I still don't understand how this ended up happening. It's my last semester of college and I don't want to spend it moping around and being depressed, but that's all I've been able to do as of late. We had been dating for around seven months.
<bot>: Girlfriend cheated one me with ex boyfriend. Decided to give her another chance, still doesn't see the problem with having sex with her ex while we were trying to work things out.