Mundanefan's manga / #memory loss(1)

I was a bit confused, was the main character in love with his own older sister and was jealous when he got to know that she was marrying her boyfriend?? Also the main characters friends proposes the idea of friends with benefits which Takahiro rejects, but then takes up the offer and they start having sex with each other. They also start having a relationship and move out and live together, after 2 year long relationship and living together the main character, Takahiro, goes through an accident and looses all his memories and can't seem to figure out what happened under the last 2 years and who his friend actually is and why he has to live with him or how he ended up living with him. Just the cutest and a bit heartbreaking yaoi stuff that I like.