Boku no Kanojo ga Eroi Wake

It's every man's dream to have a group of women tending to his sexual needs. But for Shishigami, a college student, it suddenly becomes a reality. First, his schoolmate whose nickname is Pochi becomes his sex slave number 1, her friend Mike becomes number 2 and lastly, the young landlord at his apartment, Tama, becomes number 3. His three girlfriends practically begin living together with Shishigami and although the stress of dealing with 3 women is sometimes unbearable, he can't complain about his every sexual desire being fulfilled.

(Source: MangaHelpers)