I guess the difference I see is that Jess was dead. Sam couldn't go back to her. But with Dean, Lisa is still alive and out there and he can go back to her, so that's why I fear the pining, depressed Dean, wishing he were somewhere else than with his brother. I've just had enough of him being unhappy and depressed, and if this becomes another wedge that comes between Sam and Dean (because Sam took him away from his apple pie life) I'm really going to be upset. They've been at odds with each other for too long and I was hoping S6 would be a fresh start for them both.