Seishun wa Sankakukei no Loop

It's a love story about the relationships between three childhood friends. A boy, Aiga Tsubaki, is in love with a girl, Chisato Himawari, who is also his childhood friend, but Himawari is in love with another childhood friend, Outa Tsurugi. In the first episode, Tsubaki, who is aware of Himawari's feelings, takes action in the hope that his two beloved childhood friends will become a couple.

(Source: Natalie, translated)