Is it normal to miss someone obsessively?

We were friends. He sometimes tell me that he likes me, however we were only friends. 7 months ago, he had to go to study to other country, then I became to be obsessive, I check his facebook's profile everyday, wait all night hoping he appears online on msn, and do things like that. Although we talk at times , it's not like before.
My life go around him, I can't stop thinking about him.
Now he has girlfriend and I think it must stop, but I don't know how to stop it.
Is it normal after of too much time ?