I think when one alcoholic pours out the other's booze it has a different connotation than when one of us does it. It's his deal, and it sounds like he's seeing first hand how distressing and disappointing it is when someone you're rooting for relapses. Not a bad realization to have.
I don't know that the guy who relapsed had a "choice" about it. From what I've heard from people who have, it's often that sober life has become unbearable. That's usually because they have missed something in the recovery process.