Responses
I remember reading months ago that it was actually Erich's wish to make up for all the abuse they gave Hari for not being Arina that sent her back in time. He wished that they could have treated her like family from the start.
Eugene was secretly in the middle of divorce proceedings when Hari confessed that she wanted to get married and leave the Ernst household...so he had to find a good spouse for the woman he was in love with and had planned to court (because she was so tired of the Ernst family that she wouldn't welcome his suit). So he had basically given up long before the wedding day.
Maybe the reason why hari went back into time because Eugene really loves her. And it specifically before her wedding because he's regretting for not confessing to her or like because she's gonna be someone's wife