junhao have a very healthy and relaxed situationship going on. even before the discussion of the group's sex lives in the fic, they are sleeping with each other, but don't disclose it to their friends because... well why should they? the others assume it anyway, since all their relationships to sex are pretty open (it's no secret that wonwoo has slept a lot with his friends, for example hao. i'd assume a post-fuck discussion between junhao is what prompted jun to ask wonwoo to sleep with him lmao.)
however, we can't forget that seokmin gets thrown into the mix at some point. jun and minghao are together at that point, but they're not extremely exclusive, and most importantly, they're friends. so when jun notices (very quickly) that hao is catching feelings for seokmin, he encourages minghao to pursue him. they don't love each other any less, even if that love teeters more on the side of platonic than romantic. but there is still romantic love between the two! and jun is very fond of seokmin, so after some solid conversations (with and without seokmin) they do work towards becoming minghao and his two boyfriends. and maybe more, at some point. but there is this kind of "jun and minghao are made for each other" sentiment binding the two of them together, and whatever happens, they're not going to abandon one another