Ano Hi ga Futari no Koi no Hate

I've decided that I'm never going to say "I love you"...

Natsu and Aki have been childhood friends and best friends since they were little. But a few years ago, Natsu's feelings for Aki began to take on a special meaning. This love is a dead end. He can' t let her find out. That's why Natsu tries to keep his distance in high school. But Aki, unaware of his struggles, starts to show more and more vulnerability. The lid is lifted on their pent-up feelings, and the special love between two childhood friends begins now.

(Source: Kasakura Press, translated)