Well, I think the moment when the boy kissed him he got a flashback of him being a student.
Apparently he was in the same situation as the boy. He was in love with his classmate, confessed but when they were about to kiss his classmate backed out and told him it's better to be just friends. So he went to the bridge to kill himself just like the boy did in the beginning.
And that's why he approached him in the first place. Because he saw himself in the boy...
At least that's what I got... I hope I helped (●'◡'●)ノ
I think it was him who rejected his classmate/friend? and feals really sorry he did cause his friend killed himself??? and now he went homo to seek vorgivness...and saved the young one
Let me share my way of thinking. Seme said "I'm sorry" which reminded Uke his past : when Uke was younger, his friend told him it was better to stay friends so Uke's heart felt broken, and because of that he wanted to die, jumping from who knows where. But he must have thought dying like that wasn't worth it, or someone must have stopped it, anyway, he's alive. Uke felt asleep or passed out while thinking of his past and having sex.Then the sound of the emergency vehicule woke Uke up. For 1 second, Uke panicked, because he was hearing the sound of the emergency wehicule and he felt Seme was not on the couch anymore. Uke must have thought "what is it, what happened, where is he, did he jump ???!". But when Uke turned his head and saw Seme sleeping he felt relieved. ( Actually Uke is a tsundere. He doesn't want to show it, but he is a very sweet and nice and caring person. And he was very affected when he saw Seme trying to kill himself because it was like seeing his past self. It didn't look like it, but Uke really wanted to save Seme )... so, I was saying, when Uke saw Seme sleeping near him, he felt relieved. But the sudden sound of the emergency vehicule had madeUke so anxious, he still needed to calm down, and went on the roof to smoke. c:
what was that at the end..? with the emergency vehicle coming through and his memory? past rejection? I'm kinda confused. but the younger seme was a cutie