I Don't Know Which is Love Manga Volume 4 features story and art by Tamamushi Oku.

Though Mei Soraike entered college dead set on finding a girlfriend, she's been getting a little more attention than she can handle! Especially from Karin, who officially confessed to her after their play went off without a hitch. Mei is ecstatic at the prospect of finally having a girlfriend, but in such a complicated situation, saying 'yes' isn't as easy as she thought it'd be...