Why do girls get so obsessed with their boyfriends?

[Petra]

It's actually a totally natural, Scientifically proven point that this happens to both genders during the first two years of a relationship or so. The rush of hormones released at the onset of a relationship "binds" the couple together as it were. It's just a means of ensuring reproduction. The girl expresses this through her obsessive facebooking and the boy tolerates it because he's going through the same hormonal rush.

This obsession calms down after two years. This is when the "spark" goes and either the couple gets bored and drifts apart or they settle down into something much more comfortable and long term. It would be a general educated guess of mine that most young women between the ages of 16 and 25 are either becoming involved with someone for the first time or seeing different guys etc and on the whole are not going past those first 2 years of excitement. If you were to look at an older woman in a similar position she's probably doing the same thing, but many older women have already settled down with their guys.