Kokoro Botan

From Midnight Scans:
During the high school entrance ceremony, Koga Eito from the special class helps Kasuga Niina from her poor health. His gentle manner captivates Niina, making her confess her feeling towards him. Thus, the trials in love of this couple begin.
As time passes, Niina finds it difficult to continue loving him since there are instances when he seems to be playing with her feelings. For her, going out with Koga may bring a grim future to her.