VonirComics

The main character only has a single love interest, though the kingdoms have many different beliefs depending on race and social rank for how many wives one can have, the ML personally only wants the one girl after she catches his eyes

Everyone in the realm is born with mana. It is just a matter of whether or not they have the talent to grow their abilities to use it or not. Those with higher mana capability are more easily able to detect others mana to sense his being different, plus the world has many types of 'mortals' in which plenty of people can exceed the normal human lifespan. So word about him was easily able to be set off as rumors at first, but after traveling with a prince that everyone knows about he became easily recognizable and simply couldn't hide it if he wanted to especially the more he used his abilities over time... I hope this helps explain it a bit without spoiling anything because things about the realm are explained more and more over time.

Thank you for letting me know about that ^^

Thank you for mentioning it, I have placed notes on each novel of mine that is BL based so that people have a heads up in the future. ^^

Yes, it is.