Responses
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http://www.mangago.zone/read-manga/mou_ichido_nando_demo/
I think this is what you are lookin for!
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I don't know if you have found yet but I'm also sorry I can't be of much help but I did find a list that is related to amnesia
http://www.mangago.zone/tag/Amnesia/?page=1
So in this yaoi manga there was a gay couple and one of them had had amnesia. Even tho he's been in a relationship with a guy (as i remember it was his childhood friend) he thinks he was dating his bf's sister. He had a ring on the finger. plus his bf isn't telling him that they have been a couple.
P.S later this guy with amnesia watches their own sex tape and recognizes some stuff..