I think I'm a bit older than most of the people posting, so I'll throw in my 2 cents.
Some guys (and girls, too) are much more interested in the chase than they are in the person that they are chasing. Once they "catch" someone, and they know that the person cares for them, these hunters are bored - and must be off on the hunt again.
And it's not that they do it on purpose, either. It's really just the way their feelings work. They want what they don't (and especially, *can't*) have, and are bored by what they do have. They spend their lives chasing love, and never attaining it.
As badly as these hunters hurt the people that they discard, they are to be pitied because they will never be happy, never be satisfied, never be whole.