
I think there's more to it than that. That four eyes plagiarist fucktard needs to be gone. I don't know about Sunbae tho'. I'm pretty sure there's some misunderstanding going on, but Sunhwa blamed Sunbae about it.

I think what's going on is that Sunhwa is freaking out, he is NOT in a good place - negative headspace, highly unpleasant environment - and he trusts his good friend.
The friend is probably making guesses and coming to the wrong conclusion of the sunbae being responsible for this incident when in fact there's an unknown party: the jealous, copycat, glasses-wearing, redorangehead - who I will further call Copycat because I don't know his name.
Now, I'm not saying sunbae didn't record or videotape previous partners and was caught watching them as good friend says. That could totally have happened; who knows?
When Sunhwa and sunbae were in the bathroom where things took a dark turn in their relationship, Sunhwa thought they were the only two in there. (I think) no one else was shown to have gone inside but maybe Copycat was real quiet and sneaky while the two were otherwise occupied. Unless he went even more creep and planted a recording device, his phone, or he's got a really good microphone that would pick up sounds all the way from the door. He also could have climbed into the vents or some shit. IDK.
After the sunbae snapped and Sunhwa was able to breathe and think, he was afraid and utterly shocked at what had just happened and the drastic change in sunbae. He didn't analyze the situation too much, a bit more concernced with why sunbae being so forceful, intimidating, and rough turned him on. He also easily accepted sunbae's apology which, BOI, NO!
And one must not forget that sunbae wanted to be out of the closet and open about their relationship.
So! Sunhwa's freaking out, denying it being him on the recording, trying to go somewhere safe (or maybe to sunbae) and being overall vulnerable. Trusted friend comes along, tells him sunbae did it, that he's done it before; add in the other points that I stated before and Sunhwa can compound it all to lead him to a possible conclusion of the (false) information being true.
Theeeen VOILA~ A great big fucking mess.
Enjoy the aftermath.
[this got really ridiculously long.... I do apologize. It was necessary though. Thank you to those who took the time to read it all. ]
Have a nice day!! ヾ(❀╹◡╹)ノ~
BITCH, WHAT THE FUCK! YOU FDJHDIUJS AHHH OH MY GOD, PLEASE DON'T FRACKING STAB MY PRECIOUS ROLLS, YOU JEALOUS PRICK!!!! I EVEN PITIED YOU WHEN JINHA PUNCHED YOU AT THE BAR, BUT I THINK YOU EVEN DESERVE MORE PUNCHES NOW!!!! AAAHHHH