Mmmh apart from The Third Ending:
https://www.mangago.zone/read-manga/crossing_the_line_1/ for sure (you probably know it already, it's a classic)
And maybe:
https://www.mangago.zone/read-manga/my_bias_appeared/ (another seme that realizes he actually loved the uke and regrets how he acted)
https://www.mangago.zone/read-manga/fair_play_fair_lover/ (kind of? Another cocky playboy seme that catches feelings for the uke and is hurt by the fact that the uke is not as into him as he thought)
https://www.mangago.zone/read-manga/window_beyond_window/ (also kind of? They're childhood friends and it's clear that the uke has always been into him, but I remember the seme regretting not acting sooner when he realizes that the uke slept with someone else while convinced he didn't have a chance)
https://www.mangago.zone/read-manga/fuck_buddy/ (another cocky seme that tries to make the uke jealous but regrets it when it has the opposite effect)
https://www.mangago.zone/read-manga/the_nameless_flower/ (different type of story but 1) same author as Third Ending, 2) seme's pov, 3) regretful seme/chasing arc)
This is so Third Ending coded. Does anyone know anymore manhwas with a similar dynamic, preferabally Seme POV too? I always eat this shit up