I Don't Know Which is Love manga volume 1 features story and art by Tamamushi Oku.

With high school graduation approaching, Mei Soraike tries to confess her love to her best friend for whom she had long harbored a secret crush…only for her hopes to be crushed. But a little heartbreak is fine—because she’ll absolutely, definitely, without a doubt get a girlfriend in college! And no sooner does Mei set her resolve than potential prospects start sidling up to her one by one…?!