the thing is, I had a talk with him recently when I noticed his performance and attitude starting to slide. I asked him what was going on and he didn't have much to say. I havn't yelled at these guys or been unnecessarily hard on them so I really don't get it. Maybe he was just burned out.
Maybe he found another job? Maybe he doesn't want to talk to his "boss" about personal issues. Hard to say when they don't actually tell you why they quit.