My girlfriend told me she cheated on me.. what should i do?

Wow, you wrote A LOT. Ok, so here's the deal. You need to ditch her, you'll find someone else. Sounds like your still in HS or young. You'll be ok, if you get back with her some many people will lose respect for you and think your just whipped. If she's banging another dude and not you.... There's a problem. It will take awhile for you to get over but you'll get over it. You should tell a bunch of people your story, so word gets out that your GF is a huge ***** and people will HATE her ( that's the least you can do). Now if you do have the to do all this your in a great postion for your next relatiosnhip.. Because all you have to do is find a girl that you wanna date.. Tell her the story, then BOOM she'll feel so sorry for you and she would never make you go through that again