"If you love somebody, set them free"
That's my advice. I really think that in this case, you have done everything you can. You've been honest, open, loving, nurturing, tender, sweet and patient. You're right: he knows you're there and that's why he can take you for granted. So, set him free.
He needs this transition time to figure out what he really wants. In the meantime, think about what you really want.
Why are all these other guys "hitting on you?" Are you just being nice or are you giving off "available" signals?
Is it possible that while you feel very attached to this guy, you also feel like at this time in your life you want to be able to date a variety of people to see what's out there?
This is a wise move in my opinion. He's made his position clear. He can't deal with new relationships at this point. I think he's being smart about taking care of himself. He's not taking care of your feelings, but at least he's being honest with you and himself (something I didn't do in college very well!)
If it's meant to be, it will happen later. You're still there, in his circle, with feelings. In the meantime, let him know that you've done what you can, and he's free. So are you!