If this question is in the wrong area, sorry, but did my best to post it in the right spot. OK, now here's the thing, I have been very close friends with this one person (I guess I call him just a person now) but anyway, we have been friends for oh, about 7 or 8 years, covered each others backs and everything, and now it seems like overnight he stabs mme in the back. He ends a friendship I had with someone else, by telling them some bulls*** about me, then he ends our friendship. I let him know how ticked off I was at him, as well as hurt, and he walks up to me and inhales real deep, like he sniffing me, and then exhales slowly and smiles. After that he says, "You're pissed at me, I know, but it makes me feel so good. Your emotions give off such a nice sweet smell." Then just walks away with the smile on his face.

This happened just today, when yesterday we were talking and having a good time, shooting the breeze like we normally do. Does he suddenly have some kind of mental problem?

I don't know why he would suddenly turn like that but it seems like he is loving seeing you upset over it so do not give him the satisfaction. DO NOT call, email or try and get in contact with him whatsoever. DO NOT ask people about him in any way. Anything about him that gets back to him will only make him gloat and feel he has something over you.
What you need to do is go out and have a good time and have fun and that can get back to him through the grapevine.

Even though it seemed like were like brothers? I mean that's how close we were.

Nothing you can do until he chooses to approach you and apologizes.
And then if he were to do that tell him first you want an explanation why he did what he did, what you did that made him so mad, etc...

Every time you try to find out what went wrong, why he is doing this, look his way, etc...
He will be laughing and smiling to himself how he has the upper hand and you are giving him the satisfaction of the joke being on you basically.