So technically Hwi and Param are more like friends with benefits, they have not said ok we are officially BF's. So no, he did not cheat. Hwi has told Param though, that he has feelings for him and I think this is why Param is feeling guilty for sleeping with Mr. han. Although I do think Param told him that he still had lingering feelings for Mr. Han? (Not in this chapter but a previous one/Idk someone correct me if I am wrong on the Param telling Hwi he has feelings for Mr. Han) and Hwi was ok with it/is aware of it. People (myself included) are just pissed at Param because he is being unfair to Hwi. Its like ok dude choose Mr. Han or Hwi? And if you're not ready for either then tell them that. At this point he is just stringing Hwi along.
So did Param technically cheat on Hwi with Han? Poor Hwi and Param you fucked up :/