The problem with that is that Hwi and Param aren't dating, their not together yet. Sure they have a plan to go on a date, but they are not dating and do not have an exclusive sexual relationship.
Meaning Param still has time to figure out his emptions and honestly fuck who ever he wants. He still has feelings for for Mr.Han and he gets horny easily so don't hate him for taking that one chance to get off
But Hwi knew Param liked Mr. Han. And he still tried this friends with benefits relationship with Param. No feelings. Now he has feelings for Param so now Param should forget his 1 year (or so) love just bcs Hwi likes him and he f*cked with him??? Hwi knew where he was getting in the beginning. They didn't establish limits in their relationship and he hasn't confessed so that's how it is. Is gonna hurt? Sure. But it's Param fault? Nope
I think I am reading a totally different story than you all, I mean why are you so mad with Param?? So what if he had sex with the other guy? It's not like he's a total stranger, Param has been in love with him even b4 Hwi appeared, besides even if he was a stranger I still son't see a problem since the uke is single and can have sex with whoever he wants