Eugene'll broke off his engagement with Rosabella, and she got engaged with the crown prince later. Eugene like hari as a woman and hari too, they never truly see each other as siblings since the beginning. Even in the first timeline, Eugene love hari so much, but decided not to tell her.
In the end of the story, they'll marry each other and have children, i think its possible for they to marry since Hari is an adopted child and dont have blood relation with them.
That's it, if u dont like hari x Eugene or find it disgusting u better drop this, because they'll end up together. It's not only Eugene, even Erich will develop feeling for Hari romantically not as siblings. Those two never see hari as their sibling or substitute for their dead sister. They see Hari as a woman.