The only thing I remember was it being a bl manga, it's school life(I think?) and they were rivals(??not sure)but they're always clashing, and suddenly the bottom travelled to a parallel universe where the two of them were lovers/dating
Iirc the uke WAS able to go back to his actual "reality" and was devastated by that
https://www.mangago.zone/read-manga/i_m_banging_my_rival_from_a_parallel_world/Might be?
The only thing I remember was it being a bl manga, it's school life(I think?) and they were rivals(??not sure)but they're always clashing, and suddenly the bottom travelled to a parallel universe where the two of them were lovers/dating