Am I obsessive?

I've wondered this for a few years now. Every so often, I'll meet a girl I really like for any number of reasons, and won't be able to get her out of my head. It's not always in a sexual context, but I think perhaps deep admiration.

The first girl was when I was 13, and lasted ages.
The second was when I was 15, and lasted maybe a few months.
The third girl was when I was almost 16, and this was really intense.
The fourth girl was March of this year (when I was 17), and lasted until about 2 weeks ago.

A pattern comes in that once I confess my feelings to them and they reject me, the feeling seems to quickly fade. The third girl went out with my friend before she gave me a proper answer, and whilst it was crushing, it destroyed my feelings for her.

The latest girl is one I've met at University (I started last Sunday). She's a Dutch girl who's two years older than me. She has a boyfriend and has been with him for five years. This hasn't really gained any steam or intensity yet, but I can see it leading that way in a few weeks/months. I was pretty down today when I realised she was leaving after the first year, and I had a bunch of intrusive thoughts about how depressing it'll be when she leaves.

I don't think what I have is a childish crush or anything. The best thing I can think of to describe it is "limerence" (use Wikipedia for an explanation). I had some sort of deep-seeded respect for these people, and whilst I wanted a relationship with each of them, the focus was never merely sexual. I sort of appreciated their personality more.

My basic question is this - is there something wrong with me? I've wondered for a few years if I have some sort of obsessive personality, because I've never noticed any of my friends feel this way.

Sorry for the long read, but thanks for reading!

What was that? Something about his girlfriend.