They drift apart soon after, having never consummated their relationship.
Aki's twin sister Aya is the reincarnation of Ceres, and she is eventually led to killing him to save both herself and Ceres and release Aki from Shisou's control. It also contains a subversion and plot device of this trope, seeing as Shisou Mikage, who is still madly in love with his wife Ceres, is reincarnated as Aki Mikage, who does not share such a "feeling".
They grow up together and technically they are family, but they are not related by blood, so nobody seems minding, and the issue is never brought up. Tetsuya Tsurugi and Jun Hono -the Official Couple- were two orphan kids Prof.