Okaa-san o Haramasete Kodomo ga Dekiru made Yattemita Boku

The protagonist is a huge mother con, so one day he uses tricks he learned from an online acquaintance on how to corrupt women, and used them on his mother, which indeed make her fall into lust. The twist is, she got pregnant, which made the protagonist feel guilty and cut everything off. The game takes places 5 months later, when the mother is visibly pregnant, and is asking to be with the protagonist once again.