I think it would be easier to see it as teasing taken too far rather than blackmail, as you can see later on Chanyoung was unsettled by how serious Hyunjin is when it comes to his crush, which led Chanyoung to back off. In other words, this whole thing started because Chanyoung wanted to prank Hyunjin without realizing what a straight laced person Hyunjin is. That's what led Chanyoung to become an absolute mess for Hyunjin, as he can't help to be attracted to how pure Hyunjin is while feeling guilty at the same time.
I'm sure a lot of people feel the same because when I first came across this, the score was a lot lower. It increased a lot near the end of season 1. I believe it was intended by the author that you aren't supposed to like Chanyoung at first, which mirrors to how Hyunjin originally perceived him, but as the series went on, you came to realize that this supposed ass turned out to be just an awkward, misunderstood, and pathetic guy. I guess my point is that, this series does a good job in dealing with situation that I normally would dislike in other series, and I think that mostly comes down to motives. Chanyoung in the end of the day is just an idiot. He didn't think things through and wasn't doing it out of malice.

I like what this becomes but I’m re-reading the official and tbh the beginning is SUPER uncomfortable with ML blackmailing MC into sex. He legit is like “do this or I’ll go back to trying to fuck your crush.” Granted MC offered the deal first, but idk in the moment it really icked me out. Still, the smut is far easier to enjoy than most manhwa, they have good chemistry and I do enjoy him becoming a complete loser simp for MC later on.