He may not be a jerk, don't be so quick to judge.
They change when they come back...
It may not be right, but when they come back, the world is a new place, and everything is different. The normal becomes uncomfortable. It is a major adjustment.
I have a cousin who came back totally different, broke up with his girlfriend.
I had a co-worker who was engaged, planning a wedding, and buying a house with her soldier who was in Afghanistan. He was the PERFECT guy. She would get fresh flowers, candy, etc., delivered to work almost weekly from him. When he came back, he was different and he needed space. He pushed her away, and she tried to cling until she finally let loose.
I have a friend of a friend who married a soldier, had a baby with him, moved to Kansas with him and started a new life. He came back from Iraq and couldn't do it anymore. They are now seperated.
My mom's fiance (before my dad) came back from Vietnam TOTALLY different. They broke up almost immediately.
I'm not saying it's right, but they change.
Don't pass judgement until you have walked in their shoes.
... Still, so sorry your DD is hurting. We ALL know that feeling.