My gf CTBed almost two years ago with SN (no autopsy, just my research, but I do have VERY strong reasons to believe it was SN).
Why is it so hard? Because it's all we know, the whole world disappears and your closed ones are left with all your stuff and their bereavement.
Who was it that said there's only one question philosophy should be concerned with and it's whether or not to commit suicide? Camus?
Anyway, my wonderful girlfriend doing it really traumatized me and changed my life forever. But I think I'm the only one that was hit by it so heavily. She'd got only her elderly father with whom she wasn't close and, idk, I think he got over it (however ridiculous it may sound - she was his only child). But in general, I think only your parents and THE very closest of people in your life are those that can't get over it. The rest of the world just moves on. However, please remember, the hurt of those you leave behind is very, very real, and it really should be given a deep consideration. Not that it trumps one's own pain, if it's unbearable, of course.