It is hard to know what to say exactly... seems like you might have two concerns, one with the death itself, and another with how it happened. Are you upset because of how your relationship with this person was? You say he reached out, but clearly that didn't help him. You say you haven't seen him much lately - were you estranged? Or was he withdrawn from everyone?
Death is the fundamental problem of life. Not existing just doesn't make sense, for one thing, and then there is the issue of "what's the point of doing anything if it just disappears suddenly one day?" When we are young, these issues just don't come up, but as we age and experience health issues and the deaths of others, it becomes personal and central.
So no easy answers. I think you have posted that you are an existentialist, here is a link about existentialist views of death <http://philosophynow.org/issues/27/Death_Faith_and_Existentialism>
I am a Buddhist, so my take is a little different. Notions of reincarnation are tricky... too often it is a cop out on the real issue, which is to deal with life INCLUDING death. Suicide is particularly problematic, as it is clearly an attempt to escape something in life, and Buddhism suggests that we reincarnate because we still have stuff to deal with in life. So if you don't like life, reincarnation can possibly be a very nasty problem - you really really can't run away.
This isn't to judge your friend - any of us might find a time in life when we can't go on, and decide to end it. I'm pretty clear where that would be for me. Not all suicides are running away, maybe sometimes life really is just too tough to go on. I saw a guy on the subway a while ago who didn't have a face. I'm not as brave as he is.
And death isn't the worst thing IMO, living in pointless suffering is. But remember: not all suffering is pointless.
One way to think about reincarnation is that something in you will continue on, but the part of you that is thinking about the situation it is NOT that part. The part that continues on is what you experience BEFORE you have a chance to think about it. When you see a friend on the street, that initial "feeling" you have before you think about it is the "consciousness" that will continue. There is a very small gap between that initial experience, and then thinking about it. Meditation is a way to notice the gap, then open it up so you can spend more time in that experience of "original self."
Here's a link to a long article on death which outlines various approaches, including the Buddhist. <http://www.accesstoinsight.org/lib/authors/walshe/wheel261.html>
And if you aren't up to reading, please feel free to message me if you need someone to chat with.
The worst day of my life was when my first cat died... that experience was invaluable to me. My father died a couple of years after, and I found myself much more able to deal with that constructively. Confronting my cat's death and the practice of meditation helped me a great deal.