Alpha-Raseo Sireo?
It's only natural that Alphas and Omegas love each other. Alphas are naturally attracted to Omegas, and the world is full of poems, songs, novels, etc. in which Alphas and Omegas promise each other eternal love. ... So, it's impossible for an Alpha and a Beta to love each other in the first place. Where in the world would there be such a crazy Alpha? After being revealed as an Alpha, Gun-Woo realizes that he likes Jung-Hyun, a Beta, and tells him how he feels, but Jung-Hyun rejects him, saying, "That can't be true. You're an Alpha, and I'm a Beta."
(Source: Lezhin, translated)