I'm not surprised. He's fresh from a war and he's very young to be getting married. Alot on his plate. Hopefully with time and some healing, they can work this out.
A Lt. Col. Dave Grossman has written at least two books (that I have read); 'On Killing' and 'On Combat' that are very interesting for any person who has a loved one coming home from a war zone.
Other useful reading is 'Deadly Force Encounters; what cops need to know to mentally and physically prepare for and survive a gunfight'. This is oriented towards police but applies to soldiers returning from a war as well.
The military unit should have a support group to help the family understand.
Too many of our fine men (and women) will feel as though they have to grit it out and 'not be a pussy'. This is completely the wrong approach.
Don't misunderstand me and think I am giving the chance for an excuse. The act of killing, especially up close, is unnatural and affects people in different ways.
Some are unaffected but many (perhaps most) are affected and the length of time in the area where the fighting occurs increases the negative effect drastically.
I understand the units are staying together now when deploying home, which is a hugely helpful thing because the soldiers can decompress with their peers who have comparable experiences.
PTSD is an insidious killer of the good life after battle that all of our fine men and women deserve.
There may be malingerers who do damage to all but it does not change the fact that psychological trauma happens to people forced to witness terrible things.
It does not have to be a trigger puller either. Someone who normally is away from the tip of the spear who is suddenly confronted with carnage can be as strongly affected.
This is a problem in law enforcement as well as war.