How dare this author make me like a ship besides Haru/Rin! :-P This is an interesting premise. Makoto and Rin get into a physical-only relationship, but Rin becomes increasingly bothered by Makoto's long-standing feelings for Haru. Makoto also seems to be conflicted about exactly what he feels for Rin.
This also contains Rin/Nitori (largely one-sided emotionally) and unrequited love for Rin on Sousuke's part.
By the same author who wrote about Naoki (single dad with a daughter) and Yosshi, the customer at the restaurant where he works.
Free! dj - Doushiyouka