There's a lot of scientific evidence that says that lack of physical contact with others - particularly with the opposite sex - can have a very detrimental effect on your psyche.
I believe this quite strongly. It almost seems like there are two different desires within me, one to just "get off" (which is fixed by having sex and/or masturbating) and another to just TOUCH women and be touched by them.
I do remember quite well a few months ago when I hadn't touched a girl for a good couple of months. I got with this girl and it wasn't the actual penetrative sex that was the big deal (though it was pretty good) it was the first kiss, the grasping of a nipple, the feeling of lying completely naked against someone.
Of course, I do think that whether or not you actually have feelings for the girl involved makes a big difference.
Now... this doesn't mean that you NEED a girl, I'm just saying that there are a lot of factors involved.