I remembered that seme’s dead girlfriend can possess uke’s body. Whenever the uke is the “girlfriend”, seme would act as his boyfriend and when uke is back to himself again, he just acted normally.
I went insane because I KNEW I had read this shit but I couldn't find it because I read it on mangarock, and I knew mangago had it because I remembered seeing it on mangago a while ago and going "huh I remember reading that on mangarock." But I didn't MARK it on mangago, because I had it marked on mangarock, but as you may or may not know, Mangarock got DELETED, WIPED OFF THE FACE OF THE PLANET, so I had to brute force finding this one.
Anyway, 99% sure it's this: https://www.mangago.me/read-manga/their_circumstances_sria/
I remembered that seme’s dead girlfriend can possess uke’s body. Whenever the uke is the “girlfriend”, seme would act as his boyfriend and when uke is back to himself again, he just acted normally.