Because he isnt. He is being tortured as part if play for being a brat. (Ie like all 17 chapters before)
In the semes eyes, his partner overdid it this time with his bratty behavior. Seme doesnt know he was assaulted, all he knows is that his brat ignored him and was MIA for hours even after calling him 40+ times. As a dom he is pissed. Only to ask and for brat nit to answer him properly which brat has done before to get under semes skin.
Marks doesnt equal assault. It just means sexual contact on a wide spectrum.
Don't think he saw marks but if he did, first thing you think about usually isnt flat out rape.
making out with someone leads to marks or full on cheating. Which are both consentual acts.
This is rape. The point still stands. Nobody would know it wasn't consentual if its not told.
Even if the seme did see the marks and gets angry , how is he to know his partner was drugged and violated. How does he know its not his partners willing actions.
If he did see it and all his partner says is "I'm sorry".... yeah ngl seems like it would make the misunderstandings worse and emotions go through the roof. Sorry also implies that its their fault.. as in ... their choice...sighh
Im just angry the author even added this unnecessary plot point for drama. Literally not needed.

why is he being genuinely tortured for "cheating" when in actuality it was rape