I can speak only from personal experience so take it for what it's worth. I spent two one year deployments to Vietnam and lost two of my closest friends to suicide. They didn't do it due to the things they experienced but rather what was going on in their personal lives at home and the attitude of the American public toward returning servicemen in general. Without going into details one guys wife was cheating on him and the other's family were terrible parents and siblings by basically labeling him a baby killer even though it couldn't have been further from the truth. He worked in the Motor Pool.
Neither of these guys for whatever reason couldn't deal with life and shitty parents and siblings. For whatever reasons they could deal with life.
My son spent 4 deployments total to Afghanistan and Iraq and lost a close friend to suicide once again due to personal reasons at home....not what happened over there. This guy was like a brother to him and still feels terrible about not being able to help him better cope.
So it seems like the problem in these cases was the feeling of long distance separation somehow caused these problems when in reality these problems would have occurred regardless if the were home or not. I believe these folks for whatever reason didn't have the tools do deal with life's problems before they ever joined the military. Just my two cents.