Neil completed his training a year before me and joined the 23rd Special Tactics Squadron. I was still wrapping up my training when an Iraqi Air Force plane crashed outside Baghdad, killing all five aboard, including three fellow special-tactics operators, whom we all knew. Neil shouldered the pain and wouldn’t talk about it. None of us brought it up, because we didn’t know how to deal with the loss. Back then, the military didn’t provide the mental-health resources that are available today, and we didn’t even know the terminology to describe what we were feeling. We were trained to be fighters, spending over two-thirds of the year away from home at military training ranges around the country. We were trained by combat veterans who were experts at their craft. Sparing no expense, we shot every weapon in the inventory and learned to field strip and rebuild our heavy weapons in the dark. We trained an average of six days a week for the entire eight months between deployments, then took just a couple of weeks of leave and deployed again. But no one was teaching us how to cope with the loss of our friends and colleagues.

In 2006, Neil and I deployed to Afghanistan. One of our airmen, nicknamed Surge, was on patrol in August 2006 when more than 100 insurgents pinned down two Special Forces teams and their Afghan counterparts in an ambush in Uruzgan Province. While Surge was directing nearby aircraft to target the attackers, he was killed by an airburst rocket-propelled grenade.

[Related: The first Marine in my battalion to die by suicide]

One of our airmen was assigned to pack up Surge’s personal effects and send them to Bagram Air Base to eventually be returned to his family. At Bagram, Neil decided we should burn Surge’s bloody body armor. We stood there holding it, and we talked about Surge’s death. Neil vented about how he felt responsible and helpless at the same time. He didn’t cry; he remained stoic as he spoke. We stared into the 55-gallon drum as we fed Surge’s body armor into its flames and talked about how Surge wasn’t required to be on this deployment. He had just returned to the United States from a deployment to Iraq with a separate unit, and he volunteered to take this trip to Afghanistan. Neil felt guilty for and hated the fact that we trained service members like Surge but then stayed behind while they were getting shot, blown up or killed.

When we returned from Afghanistan, I felt that Neil had lost his sense of purpose. He withdrew from his friends and colleagues and cared less about following the rules. He missed the flight home with the squadron and instead, without informing anyone, took a flight with a friend who was part of an aeromedical evacuation unit. He was given a letter of reprimand, but he didn’t care; he had already decided to separate from the service.