Help me find this BL pls!

Guy was like rivals with this one guy, then banged his head i think? And when he woke up he was in the middle of say gex with that rival because he was isekaid in another universe where they got together and at first he was like confused i guess? And then time pass he realizes his own feelings and stuff happens yk and he got sent back to his old universe where he meets the guy again and i think he likes him back as well???

please if this is familiar, reply...thank you in advance.