Onedari Milk Princess

A lot of girls contact a mysterious disease with only drinking semen as cure. For such girls semen becomes unbelievably delicious. Main character helps his childhood friend in the Milk Princess shop that supplies ill girls without boyfriends with the right amount of semen. Protagonist also participates in the "seating parties" where he gets not only blowjob, but also sex.

[From vndbreview]