Is this weird... obsessing over random people?

Ever since I was a child, I have found one person and become absolutely infatuated with her. I'm a girl, and it has always been a girl close to my age. It is also always someone I know. It's creepy... I will do anything for my current infatuation... buy them anything, try to act as perfect as possible, try to spend as much time as I can with them without being overbearing. I've gotten it down to an art. And I always end up good friends with these people, yet I still have these weird obsessions. Is there a name for this disorder? I know it can't be normal, and please don't tell me it has something to do with self esteem. I have a pretty big ego and am confident with myself and my actions. I'm really normal aside from this actually: intelligent, good-looking college student with lots of great friends. I have nothing to complain about in my life. I just have weird obsessions with an individual, then "conquer" them by making them a good friend, and move onto someone else. It's hella weird and I'm just wondering anyone else's take on it... why I do this, are there others out there, is there a name for this. Thanks a lot for your input, I really appreciate it.