Aiomou Hito - Sex Friend
From Divine Sanctuary & Midnight Scans:
The Senpai that I liked so much had a girl he loved. No matter how hard I tried, I was second place in his heart. That’s when I started to go out with my classmate, Haru, who was also having one-sided feelings. We started going out to empathize and sympathize each other’s feelings but slowly, change was starting to take place in our relationship too.