Futari no Erika ~Osananajimi to Imakano to~

Kentaro had an old friend, Erika. She used to live next to his house, but her family went abroad on business. Just before she left, they promised to meet again and marry. A few years later, he is now a university student. He lives alone and has a girlfriend. Her name is also Erika. He enjoys his university life with her. But one day, a girl suddenly cuts in. Yes, it is his old friend, Erika. Their battle for Kentaro now begins....

[From ErogeShop.com]