My girlfriend cheated on me with her Ex but now wants to be back together. What should I do?

Don't waste your time on her. If she loved you, she wouldn't of done that. Having sex with her was a bad choice, because she'll see you as vulnerable. And who's to say if you guy's get back together, she won't cheat on you again? It'll be getting more into a mess. So I think NOT getting back with her would be better for you.