The closest friend I had who committed suicide, I hadn't seen for a couple of years before he actually did it -- he was a former co-worker, I'd changed jobs, and we only kept in touch sporadically.
I do know that he was on medication, and he'd changed his life radically trying to escape the depression, but apparently it just kept following him. The ironic thing was, if you didn't know him well, you'd think he was the happiest fellow around - always a joke or funny story.
He was the classic Sad Clown.