I'm going to start from the very start. Early 2019, during the breaks at school I always look out for new people. There was a girl (we'll call her CONS) and, at that time, her (F16) friend, (we'll call her CAM). For around a month I wanted so badly to meet CONS, but I have never had the opportunity. In my attempts to get to know her name, I did a lot of research on the school list of students. I got one name, but many girls with that same name, so I proceeded to Instagram and search. That led me to two girls: CONS and POLV (F14). I had my suspicions about CONS' Instagram, (didn't know that was the one person I was looking) and we talked A LOT. I just felt in love with the things she said, the things she dreamt of and I just wanted to meet her in person. When we finally agreed to meet at one break, (back in June 13) before a show I was presenting to everyone. I saw the girl I liked to see at the breaks and a "friend" of mine got to talk with her. I didn't know what to think or do, so I did nothing to stop them. When we've got to the classroom, I asked my "friend" what the duck happened, he said that they where just talking. There was when I realised that the girl I liked in the breaks, was the same that I liked online. ONE WEEK later, I saw by accident this guy's phone, and they where talking cute, with hearts, love faces, etc. I asked him holding tears if him was in something with CONS. He said yes. My heart and hopes were crushed into smithereens. I stopped messaging and started ignoring her. They lasted around a month, maybe? I discovered, again by accident, that they where exchanging intimate photos. I felt disgusted and enormously sad. They ended because she "realised" (another person told her) that this guy was a sort of assh\*le, because he colects intimate photos of many girls, (I absolutely did NOT know that he did/do that until that very day.) I felt sorry for her, so I agreed to talk again. We gained confidence and in late July I send her hints that I liked her. She always replied with either a meme or a Whatsapp sticker, that bring me down massively. Anyways, without anyone knowing it, she wanted to try again with one "ex" (they wheren't a couple, but they had strong feelings) that she had during the summer. I felt down and just wanted to cry. Here is when CAM takes place, I met her accidentaly on a bench waiting for the bus. We've got so confident in ourselves that we taked a lot in a couple of weeks. After told me that they were friends but not close ones, she confessed to me that she had a lot of negative feeling towards CONS. A couple of days later, CONS "ended" with that "ex" and told me. She wanted to meet again during a break, and I accepted. She wanted me to ask er question, but I just wanted to know what in the bloody hell happened with the first guy (the assh\*le) and the second guy (the pseudo-ex). She was brief and told me that they wanted her only to get something about her, and again I felt sorry for her. Later that day, I met with CAM and told me various things, and one that creeped me out. "She is not with anyone anymore, it's your time to teach her a lesson. You say that you want her, you f\*ck her, and then dissapear." At first instance I was totally grossed out, but I thought about it and I, said yes to her, while in fact, I wanted CAM to think that I was going to do what she told me to do, because that was the only way that CAM would help me to reach CONS, because still I wanted a full-time relationship, not just sex or sexual behavior. Everything went okay, CAM still believed that I was actually going to do her plan, but I didn't. September 6th, 2019: CONS and I were officially a couple. During the first month POLV (a girl that felt attracted to me, wanted me to be his bf and almost forced me to be a couple) messages me via Instagram asking me if I'm with CONS. I asked why and she said me that CONS, during our relationship, was sexting with a trans girl (FM19) from Spain and yet again, they were exchanging intimate photos and messages. POLV said me many worst things about CONS, and I was stunned. I thanked her and procceded to block her. CONS and I had a conversation about the trans girl and she broke into tears. She thought that I was about to end with her (she was not wrong) but I abstained. I forgave her, let her now that everything is ok and I won't leave her side (after all, it took me so much to get her). Nothing memorable happened next (at least from my knowledge). Flashforward to four days ago (January 18) she told me she felt bad because we haven't seen us in a whole week, and I felt sorry to. January 19 she said that felt bad for gaining a little bit of weight. January 20 came, she said that was tired of everything and everyone. I asked why, she responded "there's someone that just wanted one thing from her, and was sex. I didn't know who him or her was, so I asked multiple times, she won't let me know. As a final resource, I said my name. No response. I really didn't even thought about me being in the description she said, but anyways I wrote a legitimate "I'm sorry" paragraph. She answered that I have to be careful with what people I have a serious relationship, because it wasn't pleasant know your intentions. I said that I didn't know what she was talking about and I asked who said her that bullsh\*t. Was CAM who told her, one day that I did't went to school. But was DAN (CAM's boyfriend and a friend that I know from +7 years) who told her, and CAM confirmed it. This was about two months now; this fact makes no sense to me because, why didn't she told me or wanted to talk about that in the first place? And thus, why did DAN know that and why CAM broke the secret that herself made to "teach CONS a lesson"? Yesterday, CONS ended with me. I've tried to trust my remaining friends, but I don't want a sequel of CAM again. So I, date January 21, 2020 came here to ask for help. What should I do? What should I not do? I already bought her a choker and Sailor Moon Manga for her birthday.

TL;DR: I lied one person so I could be with my gf, that person told my gf and now my gf thinks that that lie is the truth. And she broke up with me for that. Need help, please help.