Love and acceptance could be another theme. Despite the husband hiding his beauty, the relationship between him and his partner might still develop based on true love and acceptance of each other's true selves. This shows that love can be more than just physical attraction.
One similar light novel could be 'My Next Life as a Villainess: All Routes Lead to Doom!'. It also has elements of unique character relationships and interesting plot twists. Another one is 'Kiss Him, Not Me', which shares the aspect of dealing with complex feelings towards a particular character.
'My Husband Has a Beauty Mole' was a novel written by an online author, Xiao Qingkuang. The story revolved around the main characters, Gu Yunxi and Jun Chuli. It was about how Gu Yunxi's husband had a twin brother. Both of them looked exactly the same, except for a beauty mole at the corner of her husband's eye. Every night, Gu Yunxi had to stroke his beauty mark to be at ease. However, she discovered the secret of her husband and brother, which led to a series of adventures. This novel was published on the Internet and was loved by the readers.
The relationship in 'Me, My Husband and His Boyfriend' manga is a web of emotions and complications. It forces readers to question conventional notions of relationships and embrace a more diverse perspective on human connections.
You might consider giving him some space to explore the manga on his own and then discussing it together. Sharing your enthusiasm and showing how it brings you joy could potentially get him on your side.
This plot is in line with the plot of the fantasy immortal cultivation novel "Poison Poison Demon Immortal." I suggest you go and take a look. I hope you like this fairy's recommendation. Muah ~😗