I know I’m a bit late, but as far as he knows, that was the first time she’s actually shown genuine interest in having sex, right? And he knew she was drunk same as him. So it makes sense that he wouldn’t want them to do anything like that at that point, because he’d see it as him taking advantage of her while she’s drunk.
It’s something she can only really consent to while she’s in her right mind, and since he doesn’t realise she’s been wanting to do it while in her right mind this whole time, he’s just trying to do the right thing here. It makes sense to me.