James knows that lecturing House about the damage he's doing to himself with drugs and alcohol is a pointless endeavor. He watches House throw back one last shot before leaving the bar. Yes, lecturing House is worse than pointless, it's actively counterproductive, but he can’t seem to make himself stop.
Other people don't understand why they're friends. He doesn't always understand it himself. But the fierce, savage intelligence, the acid sense of humor, and – above all – the desperate neediness that House tries to keep buried: all of these things have James hooked.
House isn't the only addict in this relationship.