What do you do when some1 who doesn't want to live due to many close deaths in their family?How do you help?

My boyfriend lost his father on his mother's birthday, then a day after his father's death, he was hanging out with his cousin(someone he sees everyday) my boyfriend decides to go visit his mother out of town and his cousin gets gunned down by gang affiliation. He was told his cousin was asking for him that day before the incident. He thinks it's his fault that he wasn't there. What am I to do to keep him from retaliating and thinking he would be better off dead too?! :[ Im hurting for him, but what role am I supposed to play, I'm afraid of losing him!!!!!