Rin and Maki are inseparable childhood friends whose relationship evolves from close to intimate when they start living together. Maki is completely devoted to him, but Rin - who initiated things - is worried what other people will think.
This is the one with the sweet boyfriend with long hair who is so terribly, terribly in love. They slap each other a lot. Some readers took issue with it; I agree it's not something you should do in your own relationship, but it didn't ruin the story for me.
Hima na no de Hajimete Mimasu.