When I Tried To Enjoy The Life Of A Neglected Husband, I Ended Up Taking The Route Of Affection!? summary:

One day, ordinary office worker Kaoru Kusakabe (28) is reincarnated into the world of a BL Omegaverse novel. Kaoru is the consort of King Allen, (Alpha) and was reincarnated as "Chris", (Omega). However, as the novel unfolds, Chris has a child with Allen, he and his child are destined to be killed as there is no longer needed Allen's first husband gives birth to a child years later... In order to avoid the death route, he plans to disguise himself as a defective Omega who cannot bear children and live the life of a neglected husband, but Allen begins to dote on Chris, whose personality has changed...