Tsun x Bote! ~Ringetsu Ecchi de Kono Ko mo Watashi mo Aishite yo ne♪~

The main character, Shoma, is an ordinary student.
One day, a girl who he loves since childhood visits him and asks him to impregnate her to avoid the unwanted marriage.
Shoma, though embarrassed, cannot resist his feelings and accepts it.
She is now pregnant and they still make love!

[From English DLSite]