Only a masochist could ever love such a narcissist.

For the past month I've had this on and off fling going on with a guy in my school, needless to say it is very physically oriented. He messages, we meet, we piece, then he peaces. I can easily say, I am his bootycall, and it is pretty pathetic on my part. Everything is on his time and his needs. The only problem is I can't seem to let go. My friends are more or less at the breaking point with me and this guy, and I don't know what to do.
Well, I'm lying I do know what to do, I stop. I let him go, and I move on. Since,I should be able to realize my own worth. I'm not cocky in any sense, but I do beleive I am worth a lot more than that. However, this one guy seems to have such a hold on me that I can't seem to do that. I can go to sleep feed up, I can wake up completely -well from what I believe- to be over him. I can rant about it all day. Then the moment I see him its over, or even if a rude remark is made about him from some one other then me, I'm in his defence. Im truely starting to beleive im a masochist. The one person that has inflicted this much pain upon me I stand by and meet every need not recieving anything in return.
How is it possible that people can have such a hold on us, when we are merely tools in theirs?