Hajimemashite, Ore no Shinyuu

Shoutarou Tokitou, a university student, shares a room with his childhood friend Rin Kazama. When they were kids, the two of them went everywhere and did everything together. Shoutarou was always overprotective of Rin, who always followed him around, but after they started living together, Rin's attitude became cold and he started playing around with women... Before he knew it, a gap had formed between the two of them. One day, they got into an argument after Rin brought a woman into the house without permission, and in the process, Rin hit his head and lost all memory of their relationship. The two decided to continue living together as before for the sake of his treatment, but Rin is still as attached to Shoutarou as in the past... but seems to have ulterior motives...!?

(Source: Ichijinsha, translated)