Suki Dakara Kiss shita no?

It happened in a sunny day right before summer. Souta Fujisawa's first kiss was with his older classmate, Chihiro Ayase. It's now their summer vacation, and yet, nothing has happened between the two of them! What's worse, he discovers that he wasn't actually Ayase's first kiss, and now regrets kissing him.

(Source: Taiyo Tosho, translated)