I think that the first kiss they had was seme confirming his sexuality + attraction for the uke. After that he propably realized he is into uke hard but the uke never took him seriously becuase he is younger. Serious tsundere issues. It would suck hard if you were into a person for years and they were into you too but it would never progresses beyond a kiss.
Well she treats him sweetly but draws a clear line. I feel for him. You don't want to fall for a person like that.