And Yet, You Are So Sweet by Takehiko Shinjo

5.20

Kisaragi Maaya, 16 years old. The first love confession of her life ended in complete rejection. She vows to "never confess to someone again" in the presence of the stoic but popular Chigira-kun, while on library duty together one day. Upon meeting again, and seeing her upset while reminiscing the past, he proposes they undertake a "pretend unrequited love play". As Maaya's heart begins to heal, her thoughts turn to them getting even closer... however she definitely can't fall in love with the out-of-reach Chigira-kun...? (Source: Mangaupdates)