Originally Posted by Khorrupt
it's literally keeping me up at night.
That's not a good place to be in.
I know this on a personal level.
What I've come to find is that when your relationship with someone goes to that point, where your life becomes unhinged because of your relationship with them, that maybe you need a break from one another.
Sometimes online friendships can become a little bit obsessive in subtle ways we don't really notice. You said your last conversation was 'only' an hour and a half long but that's actually quite a lengthy time to speaking non-stop with someone. It may seem like nothing if you've been having 7 hour long chats with them everyday of the week, but it really is a pretty substantial chunk of time.
What I am saying is coming from personal experiences with different people over the years and my relationships with other people are clearly not going to be the same as yours.
You mentioned that he goes 'offline' when you come on facebook, perhaps you could try to just send him a personal message to the effect of:
Haven't spoken to you in a while! Seems like everyone's getting busy these days. Anyway I just wanted to see how you where doing, anything new going on? Talk to you later
Your leaving the door open for your friend to respond, you are saying that on his time and in his own way he can send you back a message without the expectation of being forced into a lengthy conversation. Your not accusing him of ignoring you, your not saying you suspect he's angry or any of that. It's just a casual short message.
You may find that something big could be happening in his life or he just wanted some space from you, and that's okay. Sometimes we need space alone from even our best of friends, it doesn't mean we don't like them anymore or like them any less but when you spend all your time with someone it get's the point where one person is just going to burn out and need their space.
He might need that kind of alone time from you right now, so letting him know your still interested in the friendship and leaving the door open for him to communicate on his own time may take the pressure off him to be in a constant hour long chat with you. He might need time away from you to 'wind down' from what sounds like a pretty active friendship.
If you make the effort, like sending him a message for example, and find that nothing comes of it then you may just have to accept that you aren't getting resolution with him. It doesn't always happen. We can't always close the book on a good note. It really stinks not to know the why of things, but after more times goes on and you become occupied with other endeavors and people in your life his choice to be absent will be less hurtful and just 'one of those things' that happens in life.