That's never how I interpreted that scene, as Bobby accusing Dean of causing him to continue to suffer. To me it came across as 'If I can keep going for your sake when I want so badly to check out, then you can damn well man up and return the courtesy.' Much like his remark to Castiel later on, when Cas had, from an angelic point of view, just become severely disabled himself: 'Quit pining for the varsity years and load the damn truck!'

There was simply no time and no room in their situation for whining or coddling; no matter how horrible things got, how tired and depressed and sick of it all they were, they had to pull themselves together and keep going. Quitting was not an option because it would mean the end of everything, for everyone, and Bobby knew that better than anybody. Making the others see it when they started to falter was his job. He wasn't, IMO, a terrible person; he was fulfilling an unpleasant but very necessary role.