He can't believe his eyes.
Elsa lied to him, about being home. Anna had been pestering to visit, and he couldn't keep up the façade without losing her.
Fucking Elsa. If she hadn't lied...
So, yeah, Hans was fully aware of what he was doing, but he couldn't really be blamed? His own wife hadn't put out in weeks, and even months before that she'd refuse him.
He'd married a woman. He hadn't signed up for babysitting a depressed woman of no use.
So really, it was Elsa's fault. Not his.