I Think About Her All The Time

Hello! I want you to give me some adequate advice on what to do with "my problem". The story is this ... Last year I literally fell in love at first sight with a girl who is from my group at university. Once between lectures I invited her to have a drink and in the conversation we asked ourselves if we had a boyfriend / girlfriend. She answered quite emphatically that she was not there, which was a "green light" for me to act ... yes, but no! After a period of getting to know each other, I decided to admit to her that I had feelings for her. I did it, and she accepted it with a smile, but she didn't say she had anything like me. After a few more weeks, I found out that she had a boyfriend, and she had one before we met ... Naturally, I reacted sharply when I asked her why she lied to me, and she again denied that she had a boyfriend. I told myself well I may not have understood correctly ... YES, BUT NO! After a few more weeks, I was told that she had a boyfriend (FINALLY HAS A FRIEND), until one night she didn't want to see me ... We saw each other, it was too late, and during the conversation she started to kiss me. I was even more confused ... We continued to see each other, each time I started to love her more and more and to think about her constantly - as if I was (and still am) obsessed with her. The moment came when we slept with her ... I thought there was really something between us now. We heard each other every day, she told me that she loved me, etc. In the summer we went back to our hometowns, continuing the chats, to hear each other, and at one point she started writing to me quite rarely, until the moment when stopped completely. I asked her what was going on, what was the reason, and she said she didn't want anything more from me, to see me and some similar "bull * hits" ... But the problem was that even when we stopped any contact between us, I kept thinking about her all the time. I don't know why I idealize her so much - and I can't explain it ... When we met again a few months later at university, everything I had managed to do to forget her, at least for a while, went to hell. We didn't talk for the first few weeks until one day she wanted to talk about the situation that had happened. She explained to me that during this period, although for a short time in which she was with me, she had quarreled with her friend and was confused - WOW, what a surprise ... She told me that at the moment she is with him again and she just wants us to be friends, she wants us to be in such a quarrelsome relationship ... OK, I accepted, BUT since that day every time in lectures she finds an occasion to touch me, caress me, pinch me, we call with the pet names he used to say to me while we were together, which drives me crazy. And I can't understand WHY? Give me some advice, because I'm really confused, I don't know how to interpret this ... I still love her and I'm constantly thinking about her ... I thought that this falling in love, longing or whatever you want to call it would pass, but no ... Thanks!