I think the relationship you have with your boss seems pretty avuncular. He might be a little too familiar with you but a lot of managers have different management styles. It's important to realize though, that both you and he are there to work.

Regarding your involvement with this other guy. One of the things that I have noticed is that rats flee a sinking ship. When someone is sinking at work, co-workers, bosses etc... will either consciously, or unconsciously begin to separate themselves from that person. No one wants to go down with the ship so to speak.

It sucks, but it's just office politics. My advice? Listen to your boss about this guy. If he's in trouble and your associated with him, then his trouble could very easily become yours too. I would back slowly away.

Work is work.