Strobe Edge, Tonari no Atashi Recommendations
Both heroines are cute and optimistic and have a similar name (Nina/Ninako). In both she is in love with a boy but when she is about to confess her feelings he tells her he already has a girlfriend. Later she ends up going out with the "underdog" who really likes her and accepts to be with her in an unrequited love. Both manga are filled with angst and have a love polygon.
Both have heroines with similar names (Ninako and Nina). Both manga focus on a girl who falls in love, but the love is unrequited because of a current relationship. That relationship is either platonic or static, while the bond between the main girl and boy grows. The relationship soon becomes a love triangle or love-"square."