Ettsen is not being a teenager or acting nonsensical, he just faced a harsh and raw truth: he won't be able to kill her and he won't even be able to live as her concubine (which he thought it was the reason she destroyed his country = her love for him). The goal of his life won't be achieved no matter what, so what does he have left? A cheating b1tch of a lover? He has no country, not a title, nor family, not someone who could care for him, the only reason he had to live it was his revenge or maybe the fantasy of her desire for him, so what reason does he have to continue living now?
At least in the past, she kept trying to get closer to him, so at least he had that, her attention and his position as a concubine, someone who regardless of everything was there, to give him some direction of action (his revenge). But what does he has now? She's even willing to give him a title and house to live with his cheap "lover". He's just lost my dudes, I agree he needs to figure it out he's feelings and what he wants.