You know he has to sleep with Nok from time to time to clear up some kind of energy in him that attracts the evil spirit and makes him even see them. Since Jaeshin has been away for a while
I mean, he already here so he can ward off any unwelcomed visitors; right after exercising a demon girl
At first I was also taken aback by the course of events, but after seeing the whole chapter I understood. This time the sex was nor for repelling evil ghosts nor due to lust.
It was pure desperation on both sides. Nok's because of recent gastness and horror. He's still terrified and needs to FEEL it'll be ok. That he's safe. And Jaeshin because he could and still can (but for another reason) lose Nok.
The thing the authors managed to convey it and show us an intercourse fueled not by desire or lust (and which was not an angry sex or a form of punishment etc.) is really praiseworthy ٩(๑❛ᴗ❛๑)۶
Why would they suddenly start fucking after almost dying? Dead boner?