I don't see why they would send him to rehab if he didn't need it, but it scarcely matters. Using controlled substances and not showing up on time are both completely legitimate reasons to terminate an actor's contract.
My extreme and oft-stated dislike of what was done with his character does not come from any special regard for the actor (I'm sure he's very handsome, but men aren't my thing) or the character (I liked him, but I liked most of them). I would have been fine if they had killed him off, removed the character from the show non-lethally, developed him, or shifted him to the back burner in a manner that showed respect for the audience. Somehow, they failed to meet even my low standards.