What comes to my mind is to ask the question "Why did he attempt suicide to begin with?" He doesn't remember, of course. Does anyone else? I can imagine that anyone who does
know is avoiding talking about it, for fear that he might be driven to try again.
Maybe there are a handful of different things, each of which would be terrible but manageable on their own, but collectively were enough to drive him into despair.
Maybe most of his friends only know about one or two of the things on the list, with the result that everyone's protecting a different secret.
Maybe none of the things his friends think
led to his attempt had anything to do with it; there's a secret he's held closely and preciously, that has served as his drive and reason to live, that went wrong without anyone else knowing about it; and even after he's learned everything his friends can tell him about his life before, the idea that something is still missing nags at the back of his mind, drawing him into the mysteries of his own past in search of it...
Maybe I should have warned you that I like psychological thrillers beforehand.