I think the new twin is the one knowing the uke. The other one was secretly in love with his brother 's friend, that's why he is irritated each time he speaks about the past ( because he talks about his brother and not him)
What seems strange is the uke not knowing the twin but well...
Okey this is what I'm guessing . So maybe the idol didn't go to school and it's his brother who went to school however seeing that they are twins maybe one day they swapped and idol went to school and met the mc . That's where it starts and despite the fact that he continued pretnding to be his brother and when his brother left he could no longer meet mc .. This his comment on pinning for his first love ?
Why an other couple ? I don't care at all about them i wanted the first pair
you're the only one then lol
I know it can sometimes be frustrating when your favourite couple isn’t in the a certain amount of chapter, but remember that they might come in to an important scene later on in the story and plus it’s just nice to appreciate the extra couples that get put in not trying to start anything just saying that i can understand where you’re coming from but it’s a manga, just enjoy all the art that comes your way!
(I havnt read the manga yet but I was looking through the comments to see if it was worth starting but your comment kinda made me sad haha sorry)