How to stop being obsessed with someone?

Ever since I met this guy I have been infatuated by him. He is not particularly handsome, but he has a charisma and charm and he made me feel nervous every time he was around. I vowed that I would have him so I put all my efforts into flirting with him and eventually after months of tension he stayed over at mine. It was very intense and he pretty much moved in for a month. Believe it or not we never actually slept together but he made it clear that he wanted to dominate me and would spank, handcuff and tease me non stop. After he moved away he cooled things off. But I haven't been able to get him out of my mind. I obsess as to why he asked his previous lover out to be his girlfriend but not me, I text him regularly in the hope we can regain some of that spark that drew us together initially...I can't get him out of my mind. He was mysterious, silent, dark and exciting and I never felt like I really got inside his warped head. I wish we had stayed together All I do is think about him and I have exams coming up and still this infatuation won't die

If he's taken, then he's off-limits. Stop texting him; cut off all ties and just concentrate on yourself and your exams and other things. Try and busy yourself; find some hobbies, do some extra volunteering. Do something besides sitting and wallowing in self-pity.
Just stop contacting him, since he's clearly not interested anymore and has a girlfriend already.

No what I meant was I am jeaous that his ex girlfriend made it to girlfriend status but not me. It has left me feeling very insecure and bitter. He is currently single.

I see. Has he bothered to respond to your texts? If so, then just continue chatting with him, build something out of it. If not, then just take the hint, leave him be, and concentrate on yourself. Although I do think he just used you to mess around with, felt a little frustrated that you wouldn't have sex with him, and left to do his own thing.

It sounds like you presented an opportunity to have a bit of fun by playing with the thought. Just someone wanting you is rather flattering, no matter if you want them in return. Unless he has explained or even addressed why nothing happened between you two, I'd say drop it like a cold fish. Either he is not interested and you are not doing yourself any favors by holding onto him, or you dropping him might make him realize he can't expect you to wait forever and thus resulting in him getting his thumb out of his ass. But to be honest, that rarely ever happens. Just for your own sake, move on and find other things to strive for.

Wth....look needy is never works. You'll have to move on. No point on wallowing in the pats. It'll hurt more.

Find a hobby...

Well he moved away and the more he distanced himself the more obsessed I became. Nevertheless he would continue to reply, sometimes extremely flirtatiously, telling me I was gorgeous and that he wished I was in bed with him etc, other times he would ignore. I haven't texted him in a few days now as I am fed up of not knowing where I stand with him (despite asking several times) and I just want him to ask me to be his girlfriend but he won't. Yeah sometimes I question whether it was just the sex he was after (we met at an event where I was dressed in very little and there was instant sexual chemistry) but we spoke for ages prior to sharing a bed and we had many deep conversations so I just don't know.

Sounds like bad news. I seriously recommend you stop texting him for a while. Stop asking him why you're not his girlfriend; it's really desperate, and he's evidently not as keen as you are, as harsh as it sounds. I've been there - not to the point of obsession, certainly, but I used to be frustrated as to why a guy I knew and I weren't together. The solution is this: just move on. Delete him off your contacts, concentrate on exams, hobbies, anything else. I know it seems hard, but you can do it. The more you text this guy, the more he can lead you on, using you for all kinds of things just because he knows you're infatuated.

I don't understand your first sentence.

Yeah I guess I just can't accept he is not interested. We were so close. He has attempted to give me a few reasons as to why things cooled off (the fact that he is not good at communicating from afar, that he does not want to commit incase things do not work ot between us and we lose our friendship) but I feel there are deeper reasons that he is not divulging because it all happened very suddenly.