I am writing a fiction story about a elite unit, SFD (Strike Force Delta), during the Third World War. The war is basically extremely variable, it lasts from 2025 to 2030. I like to call it the 'mixing pot war' because all of the theaters of the war mimic previous wars in that area. Instead of having nukes, the countries use a myriad of nerve agents and other poison gases against each other.
The story is written from the point of view of the Sergeant who leads the squad. In the end, all of his men are killed in a horrendous battle and the squad is awarded a Medal of Honor for their actions before they died. (The men don't all die at the same battle, BTW).
Currently, the men are stationed in Passchendaele, awaiting the General's orders to attack. There is a character who is in the squad who knew the Sergeant before the war, and married the Sergeant's college sweetheart.
How do I write the Sergeant's POV without making him a angry guy but still resentful toward the character? The Sergeant is supposed to be a hot-headed laid-back guy. So how do I write this so as to keep the Sergeant's personality?