
Tbf, at the perspective of the 3rd party, it's not exactly a lie. He said what he observed from all the interactions (and limited info he has) Maybe it comes from a good place but its just that the info he gets are limited so he jumped into the conclusion that uke doesn't like the seme at all. Anyways, I'm not blaming the leads especially the seme for feeling that way because its completely valid. It's also the effect of all the postponed and swept under the rug clarifications. Overall, they just have to communivate their feelings and for the 3rd party(seijun) to pipe down a little bit.
the seme didn't kissed the other person, he was forced, he was even forces to go into rut
the other omega said very directly that he was doing all that to get a reaction from them both
the seme is not mad because his lover is not jellous, his confuse, because THE OTHER OMEGA (the one that has being FORCING himself into the alpha) filled his mind with "your partner doesn't love you" "i've would never reacted like that" "so cold, are you sure he loves you" IDEAS
his not being "way too dramatic"
because yes, they work in the same industry, they have already talked about this, BUT a third party has being feeding him lies and insecurities, so he expected some positive response from the uke (like a "don't worry, i know you love and i love you" or a simply "ew~ you got yourself a weird work partner")
he expected to be reminded od their love, not just some "don't let that affect your work"
SEME WANTS THE UKE TO SEE HIM FOR MORE THAN JUST AN IDOL!!!
he wants to be himself, his partner, the one he loves, instead of a coworker whom he sleeps with
if you want to fight someone
FIGHT THAT WEIRD AD OMEGA, THAT'S SO FULL OF HIMSELF, TO THE POINT HI STICKS HIS NOSE IN OTHER PEOPLE RELATIONSHIP