Houtou Sennyo ~Amai Shiru no Yuuwaku~

Main character is an ordinary student. He dates a cute girl Nana for over a month, but they aren't even holding hands yet. One day a loli girl appears before him. She claims to be a goddess of love and sacrifice who came to help make his ambitions fulfilled. She passes him a pill saying that it will help make all the girls he likes belong to him.

[From vndbreview]