! Luke looks pretty fucked up. Maybe it's not only the loss of his students. Maybe he let the rage take over him and then carved Snoda up in what he is now. You know, all those years of enlightenment and he still let the dark side take over for a while.
! Nah, he just looked depressed.
Personal failings and dark side are involved sure, but I think it's pretty clear it's all related to what happened with Kylo Ren.
He tried to pass the torch and the torch exploded.