Naturally, we don't know all the facts from just one post, but here are a few genralities I've noticed, maybe one or more will apply:
First of all, this is one of the many cases where I feel it's not a "guy thing" or ar "girl" thing", it's just a "human thing". We want what we don't have, and if you make yourself too available, you may, in fact, lose interest. I'm sure it's happened to girls too, which is why they're attracted to the "bad boys" who are a challenge to tame, rather than the "good guys".
And here is one where gender DOES matter, I think: Guys do tend to run away from commitment more often than girls because we're not ready to settle down until much further into our lives as compared to women. I don't know why, maybe we just don't hear the biological clock ticking, should we want to have children..that's one of my theories. Maybe it's tradition, I don't know.
BUT if we happen to come accross "THE ONE", where WE fall head over heels, naturally, we'll be ready to settle down with this one. If feelings are reciprocated, then there's the match made in heaven, if not, the girl doesn't feel the same way, then it will be a guy writing your very same post, asking why women push a guy away when he gives himself completely.
I think, in the end, it's compatibility. If the guy is ready (and looking) it'll increase the chances of him wanting to settle down with you and have this kind of close relationship. If he's not ready, than this is, unfortunately, a sign that..he's just not THAT into you :S.
Give him no more than he gives you..if it's not enough for you or not what you're looking for; move on. Who knows, maybe if you move on he'll realize he doesn't want to lose you :).
