What a terrible day for you, all his friends and most of all for his family.
As many have noted here, it is impossible to know what would make a man do that, but an outwardly brave face can easily mask depression or despair, and we men are so bad at talking about it or asking for help.
Having dealt with too much loss in my own short time, I have some inkling of what it's like, and my heart goes out to all of you.