@ Hera - For your item #1, I don't confess this very often but I was like this once. I was about the same age as your friend and was literally batshit crazy for a girl. I was doing everything I could think of to get her to love me back. The result was that I was pushing her even further away, which in turn made me even more desperate to gain her love. I didn't notice it then, but I was also pushing my friends away because all I could do was talk about her, and they were getting sick and tired of hearing about it. I also didn't really listen to anything my friends were trying to tell me about letting her go.
As time went on I grew up a little more physically and emotionally and realized that what I was doing wasn't helping anything. I looked at things from her perspective and saw myself as she must have seen me, and it wasn't pleasant. I also came to the realization that I was never actually in love with her in the first place, but rather, I was in love with the idea of being in love with her. I learned a lesson and this allowed me to move on. My friends came back, or rather, I came back to my friends.
I know this will sound blunt, and I'm sorry about that, but your friend is young, and, while I sympathize with what he is going through because I've been there, he needs to grow up some more before he can find the one he truly loves, and will love him back. Keep talking to him, but unfortunately I doubt he will listen to you. Just be there for him when he snaps out of it.
EDIT: Don Q and Paranoid Android say pretty much the same thing I did, but were faster on the keyboard.
Endless "Batshit crazy" Soul