It was volume 6 part 6 or 7 if I remember correctly
Spoilers
So basically what happened was ml does stuff to mc but no penetration takes place
It's kinda downplayed here but mc is kinda traumatized by the whole thing, for that moment at least
When melmond wakes up and goes to where the mc is, he saw the mc sitting there half naked with a dazed expression and then melmond thinks that the whole room smelled of semen strong enough to birth 10 children lol
I really recommend the novel cuz it's much darker
They have kept things pretty mild in the manhwa
The ml in the novel have a much darker personality
If there's one downside to the novel then it's the fact that ml rapes mc and also SA him a few times like in the latest chapter the library scene was definitely a SA

I remember this scene from the novel
Ummm
let's just say it was wild