I just don't believe anyone can ship Shun and Dai at this point so far, unless it's because they're young and "cute" and there is height difference... My opinion.
while it's important to be attracted to each other, it's clear that Dai is easily swayed by a handsome guy and looks are super important to him, which doesn't make him a bad person and it doesn't mean he's a cheater of course, but for me, it kinda makes him a red flag and he and Shun wouldn't work... I would be extremely shocked in bad way, if they ended up together...
Well, what reason there could've been, really? Why would someone get him on drugs, when they didn't have a reason, you know? And some people, just like the culprit, simply don't need big reason, they just do it. Better than forced sob story for me. It felt fitting to the drama.