<human>: Condense the text into a few key points

We've been together since about July but really began dating in around October. We lost our virginities to each other in December and have been having sex snice. This is my first serious relationship and I have no idea what to do. I love her. She's been lying to me for at least 3 weeks. She got extremely strange around when it began and wouldn't see me and would barely talk to me. Turns out she had been hooking up and having sex with her "best friend" (15/m). She lied to me the entire time and always would say there's nothing between them and that she is just going through something. Then a couple of days ago she admitted that he was really into her but that she didn't to be with him and she wanted to be with me. It seemed like he was either making things difficult for her or had tried something with her and I was going to kick his ass. I fb messaged him because although I don't know him, we sort of know who each other are. I decide I wanted to be polite since I was already planning on fighting him. Here's the important parts of the conversation with him  I'm on the phone with her as this is all happening, so I don't have screenshots of that. At first she tried to cover it up, then tried to minimize it but then just admitted to everything. I went into a rage and broke some things, then was just miserable. This was today when she was trying to check up on me  Some of my friends/people who are aware of the situation say that I should never talk to or see her again. Others say that it doesn't necessarily have to end but she has a lot to do in terms of trust and time/space for me to heal. I feel utterly broken and I cried until I couldn't anymore. I see her tomorrow anyways and she wants to talk in person. I don't know what to do.
<bot>: My girlfriend cheated on me and lied about it but it doesn't look like it has been for long. I don't know what to do