This is on the assumption he’s not married:

Scream and run away then sit quietly and hope to god that Tevruden doesn’t want to kill him for sleeping with Feiyn.

He would feel bad about screaming and running away. Probably send some tea to Gany and hope he never talks about it.

Here’s how I imagine the conversation with Tev would go:

Varaelian: I woke up in bed with naked with Feiyn. I think I slept with her pleasedontkillme. 

Tevruden: Oh, is that all? Her clothes weren’t stolen or anything were they? We were supposed to go hunting later.