If I was barely surviving in post-apocalyptic zombie Georgia, and my wife just died giving birth to our baby, who fills the prison I'm living in with cries every night, guaranteed I would be having emotional problems dealing with it. My mind would cling to anything I had in life before that was good...and my wife calling my name in lingerie would be on top of that list.
As for the whole "it's Lori's fault" argument for Shane being a complete whackjob. That isn't true either. Dale caught Shane aiming his rifle at Rick early on when they were camped out at the rock quarry. Shane could have went for Andrea (who liked him), but didn't. He was always a bad seed who would turn on anyone for any reason. He had alienated everyone in the group (except Andrea and Lori) with his back-stabbing ways, before finally challenging Rick to a duel.