Well about him being devastated I'm not 100% sure because he is really good at acting and manipulating, but that's another thing. Rereading the whole thing again I noticed that Kyunghee behaviour before the stalking is not really clear (like just a few panels?) So I don't really understand his old relationship with the director. But if the director said that Kyunghee was with him because of his money and his power, doesn't that show that he already knew about it and he was fine with it? At least this is how I understood it?
There isn't really anything pointing towards that he knew Kyunghee was using him, what i got from that is that he was looking back on his relationship with Kyunghee and realizes in hindsight that Kyunghee was never really in love with him. I think the same thing Kyunghee did to Junsik is what he did to Sihyun, he seduced him, played to the guy's growing feelings and then dumped him leaving him wondering why. In ch 21 the way Sihyun talks to Junsik makes it seem like he's been in Junsik's shoes, he even says "don't flatter yourself into thinking you know what's going on". He knows Kyunghee is using Junsik because he's been there before himself, he knows Junsik "doesn't know what's going on" because he didn't at the time either. They were blinded by love to Kyunghee's intentions. When i say "devastated", i mean all the stalking/blackmail/rape. They seemed to have been in a more tame relationship before all this, then Kyunghee dropped him leaving Sihyun devastated and doing all this just to keep Kyunghee.
He is not the victim! He entered a consensual relationship with both men. And both relationships went to shit because he was using them. It's not his fault that CEO director dude caught feelings and became obsessed but c'mon. He encouraged the other guy to kill CEO. He is not a victim.
Kyunghee these shits keep on happening to you because you date crazy possessive creeps #－.－)