I’m sorry don’t take this in a wrong way but I think it’s just because of the omega’s pride. Since the beginning, he always likes the blonde and wanted to be with him, protect him, and even promising as mates— thinking he’s the Alpha. However, after their secondary gender, his ideals were crushed. It’s more like self hatred (can’t accept he’s an omega) or pride.
Yes, it was set on his mind that he will be the one protecting the blonde one, only for him to turn out to be the omega afterall which ruined all his plans. Might be the reason he became into judo to regain his own control with his life again. That’s why I don’t think it’s ‘forced rs’ cause in the beginning, it’s already there. It’s just that it didn’t go as they planned due to their secondary gender.

I guess its hate to love, BUT, i feel like their relationship will be forced by the author. The omega clearly doesn't see in alfa his mate and the only reason connecting them is pheromones compatibility. I dont think its a good ground to raise a relationship.