We basically condition our soldiers to behave in inhuman ways for the sake of "the mission", and we expect them to somehow retain all mental faculties. Despite overwhelming numbers of veterans coming home with PTSD and other debilitatations, as long as they can "keep it together" while out on the field, they're fine - otherwise they get life in prison or the death penalty.
The military can only operate if the troops "keep it together". You can't compare the military world with the real world. They're two different beasts.
If he were really having issues, he could have spoken with his chain of command or his chaplain. It would be ignorant to say it would be easy for him, but he did have channels. Instead, he abandoned his guard position, leaving his friends vulnerable. And then, they had to conduct search and rescue operations to attempt to find him.
There are different standards expected of the military, because they operate under different circumstances. If the military let everyone who just wasn't feeling it quit, it would fucking collapse.
Now, had he been completely fucked in the head upon his return (like babbling nonsense), then maybe we could look at it from a different angle. But as far as I see it, he did something fucking stupid putting his friends at risk. I have no sympathy.