
Probably because Alex keeps pushing past boundaries DG didn’t know he had until things went too far, too. Like the scene when they were almost caught in the student council room, or with the toys. DG was uncomfortable with both and Alex ignored him. Like, yeah sex with his idol is pretty great, but I think soon he’ll get to a point where DG realizes he can’t trust Alex (if he isn’t already there)

Interesting! Here are my 2 cents: I believe that what MD has against Jiwon is that Jiwon was brroadcasting and telling dirty stories when he's actually a virgin. So the night they went out drinking he confessed to the truth+ had sex for the first time and with that person showed in the flashback.
Concerning DG, i 100% agree with u. You know what would be nice? Jiwon falling for DG and confessing to DG but DG rejecting him because it is Alex who he likes; not Jiwon...

Anther thing: maybe DG asked Jowon to go out on a date with him just to fulfill his fantasu of boyfriend-Jiwon and then break off their arrangment b/c he's getting hurt... then Jiwon will start doing ALL THE CHASING ╮( ̄▽ ̄)╭

DG realizing that being just sex buds isn't enough and the mistreatment and attitude from Alex is painful. Alex is insensitive and inconsiderate, selfish...anyways he has issues. That panel was the face of DG slowly losing his patience, building up to the day he will walk out on Alex once and for all. We will see more of DG's hurtful expression until he has had enough. Alex will not be treating him right any time soon or if he will it will be until something happens.
According to Google translate, after Alex tried to push off DG's head from his shoulder, DG says he is tired and Alex gave in. That look from DG when he said that might have shocked Alex, since DG usually is someone who doesn't make expressions like that or someone who doesn't get pissed easily.

It's not that he's tired, it's that he "had a hard time" referring to how Jiwon treated him roughly during sex last time. So, basically making Jiwon feel guilty. I think it's definitely disappointment.
One, I THINK I might know what it is MD has against Alex. In the last panel, it shows Alex getting very pissed at having been beaten by DG in a game. My guess is that he actually has anger issues and it got him in trouble in the past. He could have been some kind of abusive lover, maybe something got out of hand? He could have also been blackmailed by someone and forced to sleep with them.
The other thing I noticed, is the slow but nonetheless steady instances where DG will actually look bummed out while with Alex. In the panel where they're watching a movie, DG is seen ecstatic being able to lean on his shoulder, but in the very next panel, we see him disappointed as he's looking at Alex who isn't returning the affection. DG is a cutie and cinammon roll, but chances are, one of these days he'll realize Alex's relationship isn't working, and he'll sadly tell him he'll have to break up/stop being sex friends with him, realizing he's not receiving affection back. I've noticed this several chapters back in the ending for chapter 22 for example, when Alex remarks "I haven't even come yet", and an indication they are going to have sex, DG, the normally ecstatic die hard Alex fan, doesn't appear to be looking quite as happy. There are other instances if you look closely at DG beginning to lose his passion