Yokubou Lock: Boku no Kanojo wa Shasei Kanrinin

The main character, Tsukasa, confesses his feelings to Tsubomi, the girl he fell in love with at first sight. Surprisingly, the answer was OK. Tsukasa was happy to have found the lover of his dreams, but... Tsubomi is such an incredibly caring person. And I'm grateful, but... things just keep escalating and she keeps craving my semen.