Question about "Before the Devil Knows You're Dead"?

I'm not very sure, either. First, I thought Andy was close to him because their drug connection. And every time Andy goes to use drug, he would complain about his life. Therefore, the heroin dealer was kind of like shrink without actual help. However, Andy killed the other user/customer, which is not necessary especially when he was sleeping. Maybe, Andy had some feeling for that dealer.