This is just crack taken seriously, ngl, but I'm feeding my own delusions. And my love for Possessive/Jealous!Gihun.
Omegaverse, canon-based, and Inhun endgame BUT! Salesinfficer used to be "A Thing" since forever and it's not until very recently that they stopped.
Maybe Inho had to satisfy his, eh, alpha needs, and didn't or couldn't take suppressants. Masked Officer (alpha) and Salesman (omega) just happen to be available; they merely offered a space in their bed to a friend. Plus, they (MaskedSales) have been a couple for so long, but they refuse to bite each other, which allows them to remain unbound and open to have anyone join them if they want it. It's a win/win situation.
Adding to the mix the classic "Inhun meeting before the games by accident" and "Gihun gets so well fucked be keeps thinking about that lovely lone alpha he had a night stand w/" Then, when he finds Salesman, it just happens that it was some days after Inho last rut—whoops. SO GIHUN CAN STILL SMELL YOUNG-IL'S SCENT ON SALESMAN, HE'S FREAKING PISSED. Salesman didn't know Inho had meet Gihun before, but oh, what a coincidence! He's on cloud nine knowing he and Gihun shared the same cock. But he also can't help but mock Gihun a little because he did get knotted many more times than Gihun did, ah, Young-il (what a stupid name Inho, you could've chosen something better) does have long ruts you see, I just had to help him. Poor thing, his cock was so sore after knotting me so much.
Later at the games Inho knows he can't use his wife as an excuse to lie to Gihun, because Gihun stares daggers on him when they first met again, Inho knows why (he wanted to die when he was watching the recording of that moment) but he has to lie and act like he doesn't understand why Gihun's like That. Just like Gihun refuses to disclose he met another omega the alpha had just fucked (or that he played Russian Roulette with that very same omega).
If later for some reason Gihun and MO cross each other, and Gihun AGAIN CAN SMELL HIS YOUNG-IL ON SOMEONE ELSE, he's losing it.
Young-il swears he isn't, but Gihun definitely thinks he's a whore. He won't slutshame him, but he's really considering the idea of making a respectable alpha out of Young-il. Maybe after he lost his first mate his brain got fucked up, Gihun will have to fix it somehow.