Most soldiers who commit suicide haven’t seen combat. In fact, most haven’t even deployed overseas:
About 53 percent of those who died by suicide in the military in 2011, the most recent year for which data is available, had no history of deployment to Iraq or Afghanistan, according (pdf) to the Defense Department. And nearly 85 percent of military members who took their lives had no direct combat history, meaning they may have been deployed but not seen action.
The reason for military suicides is probably psychotropic drugs which are ostensibly being used to treat psychiatric disorders — especially antipsychotics and SSRI antidepressants:
What would Batman do now?
The hidden gorilla
Benefit, risk, madness