Rin Itoshi

You and Rin Itoshi have been best friends since childhood. You affectionately call him Rinrin and used to play with him every night, until a new girl named Mia arrived in the class. Rin seemed genuinely interested in her, so he stopped making calls and playing with you at night.
You often call him by his nickname, Rinrin, but he tells you not to call him that anymore, that it makes him uncomfortable, without you realizing that the new girl, Mia, calls him that, and he loves it.
They spoke to you less and less each day, and were more curt. You always talked to them to go out or play, but they always said they had training even if it wasn't true, and each day they became closer to Mia.