It's has a novel.
Here are some spoilers
he's not an omega, he's a beta, a special kind of beta, a Diamond Dust, which means he's a fated mate for a ghost alpha. A ghost Alpha is an alpha who while knotting a beta releases a chemical that alters the beta's body, transforming it into an omega. This process is gradual; the more knots are struck, the more the change occurs. Liu is a golden and ghost alpha.
Diamond Dust betas releases pheromones that only its ghost alpha can smell (that's why Liu smells Yeehyeon and thinks he's an omega). At the same time, Didi (diamond dust) can smell the pheromones of its ghost alpha (that's why Yeehyeon can smell Liu's pheromones even though Liu is a Golden Alpha).
A diamond dust and a ghost alpha are rare; they're like unicorns There isn't much information about them. In other words, Yeehyeon and Liu are destined mates, made for each other
Each time he knots him, he releases chemicals that gradually transform a beta's body into an omega's. With each knot, Yeeyheon's body changes; he knows this because he's a ghost alpha. Before Yeeyheon, he had never knotted anyone or wanted to, but every time he has sex with him, he knots him, multiple times, as if his body and Yeeyheon themselves demand it. He knows it, he knows it's wrong to do it without Yeeyheon being aware of it, but he's afraid Yeeyheon will leave him, and that's exactly what happens. He doesn't tell him; Yeeyheon finds out from someone else. They don't end the relationship, but they separate for two years. In all that madness, knowing he's doing wrong and not being able to stop, he ends up doing things that are out of character for him, like asking Yeeyheon to marry him, wanting to open a Phontom branch in the USA, wanting to take Yeeyheon to the USA, separating him from his family and friends in Korea. He knows it, and he knows he's doing wrong, but he's desperate.
He may seem rude, but that's just his personality. Liu is a Golden Alpha, and to be one, he needs rigorous practice and exhaustive control to manage his pheromones, never releasing them under any circumstances and never letting himself be influenced by other people's pheromones. He has a very close circle of friends: Shushu, Inwo, Juhan, Yuni, and Director Han. Although his work brings him into contact with other people all the time, these are his true friends, and it took him a long time to form these bonds and let them get close to him, especially since he's a Ghost. He also has a whole family history related to this, a rather sad one that left a lasting impact on him. It's why he's so affected by and admires the painting Yeehyeon did so much. He went abroad to become a Golden Alpha, and that had an effect on him and how he relates to people. From the first moment he sees Yeehyeon, he feels attracted to him not only because he's his Didi but also because he likes him and senses his pheromones. Yeehyeon keeps saying he's a Beta, so Liu thinks he's lying, but the attraction is so strong that he can't stop thinking about him. He's cold on the outside, but from the next chapter, where they're together for the first time, he starts to dote on Yeehyeon, loving him and being incredibly affectionate.
And what he do to Yeehyeon to be apart, I explained it in the comment above, it's easier to read there than to rewrite it all, which would make the message way too long.

Is he really not a omega???? Can someone spoiled me? Idk if it has a novel or not