4 and a half years ago, whilst in the army I woke up at 11 o'clock in the night. I had guard duty from 12-2 but woke up due to the noise. A fellow soldier in the same camp as us, but belonging to the unit next to us, had shot himself below the chin with the bullet going into and out of his skull.
We found out he was a straight-A student, scholarship to uni after his service, karate national champion, with a girlfriend.
Everybody was confused as to why he would commit suicide. The only thing was 2 minutes before he did it, whilst casually texting his girlfriend, his last message was "I can't take it anymore". An unopened message was found onhis mobile from his girlfriend, saying "don't do anything stupid".
Turns out he couldn't stand the pressure, but he didn't tell anyone anything, he didn't show anyone anything.
I believe, having no one to talk to is a big reason for these things. I don't mean he didn't have anyone to talk to, just that he wasn't so open-hearted as to trust his feelings to his fellow humans.
Whatever the case, it is wrong, because it affects everyone else around you.
I'm deeply sorry for your loss, but the best thing to do, is to stop asking why or any other question you might put as a burden upon you.