there's a manga that was like this, he was an alpha then he was becoming an omega. he went to the doctor to ask why he got wet and he said it was because he was treated like an omega, his seme(alpha) likes to release inside of his ass, biting his nape whenever they have sex and everything. The manga title is Imitation Mate
see, imitation mate had a great storyline! it was consistent and original unlike this manga that was just bad. it had great potential but was executed horribly. the author was trying too hard to be original that he/she completely crushed the storyline. the pacing was terrible & too much information & drama coming out of nowhere. it's really a shame bc the art was breathtaking.

Honestly it was really rushed and how he turned from an alpha to omega is..? :/