i love how commited you are to me answering this akjsb bc i saw your comment waking up this morning and opening retrospring i thought i had hallucinated the comment was on ao3 but FOR THAT (and bc you've been awake all night pls rest) i'll kind of answer even though they'll be a much clearer answer in a couple of chapters
if you think back to their conversation in valentine days when hyunjin and seungmin kind of officially called things off for good seungmin implied that hyunjin had feelings for someone else and in that conversation you're talking about he's simply wondering why he doesn't fix his shit with that person instead of going for strangers hope that clears things up!
I'll also post the parts i'm referring to as a reply on twitter! i'm sorry i can't answer this in detail but again you'll have an actual answer in a couple of chapters i hope this can ease your mind in the meanwhile aksd pls rest well <3 and thank you for caring so much as well!!