Dude That guy's drugged. The ML is drugged too. If he was in his right mind he wouldn't be fucking the MC, the MC just has a worse reaction because he's having suppressant withdrawals, just because the ML seems to be in his right mind.. it doesn't mean he's not affected.
I mean I didn't think ml was? He says what he's reacting to is mc's pheromones, not whatever is in the coffee. He's not drugged, he's just horny cuz of mc, like when he drove him home. He at least had it together enough to walk away before he changed his mind. To me, it seems like he's only going along with it because he's a fuckboy and mc asked.
There were enough context clues to literally conclude the ML is being affected by the drug. When it took effect he literally started texting his fuckbuddy until he saw that the MC looked off—we can also see him try to resist.. and that line where the MC says "you're warm.." someone being in rut/in the verge of it will have their temperature rise. And in a writing perspective him seeming like he's a fuckboi in his monologue seems quite intentional, the plot of heat/rut cycle makes people lose their sense of rationality and literally focus on mating. but I'm giving the story the benefit of the doubt there.
"You're no fun"? "You're no fun"??? Did you forget mc was drugged? He's not having sex with you "for fun". God i hate this ml so much. First he makes a big deal about how "i'D never slEep wItH HiM" and "I cAn't lOsE mY rEfuGe" only to turn around and fuck mc the second he gives him an iota of non-platonic attention. And then he treats him like another fwb during. I'm so sick of these authors making mc pure as the driven fucking snow while the ml is running around sticking his dick in anything with a pulse, including the friend he's supposed to cherish. God I need there to be a second ml or something. I want this obnoxious manwhore to get cucked soooo baaaaad please someone tell me this happens.