I hate how I can't watch it when it shows. Damn you, 5 am wake-up time!
SPOILERS... in case you didn't watch the first hour yet(?)
Actually, I feel sympathetic toward the partner. Before the dead started walking, he had a girlfriend even if they did have a few minor issues. She's probably dead or left him during the chaos. He and the wife are rightfully assuming he's dead, so they've clung to each other for physical and emotional survival, even being self-aware enough to hide their possibly confusing sexual relationship from the son. I think the partner honestly wants to take care of his partner's wife and son, not really just taking advantage of the situation.
Then again, if they'd been fooling around before the shooting, they're both douche bags.