Himawari no Natsu ~Boku ga Eranda Ashita~

Main character confesses to his classmate Mayu, and they start dating.
Three months later protagonist meets another girl Mayu who can't find her parents. For the time being hero shelters her at his place. As he starts to ask around, his girlfriend Mayu changes appearance somehow. What's the connection between these two Mayu girls?

[From vndbreview]