Dear H & C,
The feelings you're going through are within a perfectly normal range for us all in an early adult relationship, but the way I see it, you've got to get this guy out of your life!
Harsh, extreme, drastic - that's the way to go.
You Shouldn't Have to Wait Around for Someone
No matter how young or old you are, you shouldn't have to wait around while a partner (especially one who's not committed to you) gets his act together, and you certainly shouldn't be treated badly or taken for granted.
I'll comment on a couple of specifics, but that's pretty much all there is to it: you need to let him go, which means voluntarily taking on some pain yourself.
Personally, I think you shouldn't have any contact with him at all for a while, because it sounds like it's wreaking havoc in your life to have him there on the outskirts.
Perhaps the biggest warning sign for me in your letter was your description of the night recently when you let him sleep in your bed drunk because you didn't want him driving home, and he tried to kiss you.
First, good for you for showing that kind of responsibility to a friend. However, next time something like that happens, unless it's your boyfriend or a male friend in a CLEARLY DEFINED platonic relationship (very much NOT like this one), either make him sleep on the floor or a cushion, or YOU sleep outside the bed.
Second, the real red flag: that kiss attempt which you noted yourself may not have been a conscious one. I don't know if you realize this (and my female colleagues can comment if I'm off base here), but in my opinion, you were very close to being sexually assaulted. I am in ABSOLUTELY NO WAY saying you asked for it, just that you were in a potentially dangerous situation that you should try to avoid in the future (refer to my points about where friends can and cannot sleep in your presence).
To be clear, I'm not saying this guy (or guys in general) are inherently violent, but he was not in control! People do all kinds of stupid things under the influence of alcohol and drugs that they otherwise wouldn't do. Anyway, his hot-cold treatment of you is indicative of his own confusion, and you each need to work on clearing your heads individually.
It sounds like you've got quite a cadre of admirers in your immediate social circle, not to speak of the rest of the world, so my ultimate advice is to take advantage of your youth and freedom and (responsibly) have fun.