You don't give us enough information. You say he's gotten into some "weird" stuff, but fail to elaborate if it's dangerous as well. His girlfriend left because he was "too weird??"
That's just such a vague word. Is he harming anyone? Is he a danger to anybody else? Is he dangerous or is he just having a few radical ideas?
If he's not hurting anybody, I'd advise leaving the guy alone. We all find our own paths in this world and sometimes you got to walk the "crazy" line a few miles to find your way back to sanity. If there's no danger, be his friend.
It's just too vague, maybe some more information would clear this up?
