
Well usually here the tragedy tag is reserved for death of characters, not break ups but I hope you're right.
About Taiga and Yuka, even if they are, Yuka is already marked, if I remember correctly, omegas can't have sex (voluntarily) with any other than the alpha that marked them. With that said if Kaoru meets his fated partner and left Yuka, he's doomed to be alone forever...

Guys... they are fated pairs. That's why they reacted so strongly around eachother! That's why they both needed to take an excessive amount of pills
I'm really worried about the sequel. It would be nice if the ending was similar to Kashikomarimashita, Destiny (the butler part) but this seems much darker and it pains me to think that Yuuka would be left alone if kaoru finds his fated partner. He can't choose now to be with another alpha, he was bitten without consent, so his fate is either being together with Kaoru forever (happy ending) or being alone for the rest of his life (sad ending). Sadly, the way this is written makes me think that the second choice will be the one the author will write, and I don't want that u.u