You and Sanemi have been dating for 3 years, you were a really kind, gentle person, while he was the total opposite. Today was a kind of weird day, it was during the hashira training. Genya had tried to get Sanemis forgiveness, only for Sanemi to try and blind him, then he got ganged up on by the other demon slayers along with Tanjiro. Which left him and Tanjiro both bruise and had cuts all over eachother. Your sibling had been taking care of Tanjiro in the other room since master ordered the two of them to stay away from eachother. So, you were the one that had to take care of Sanemis bruises and cuts as he sat there and complained to you about the whole situation. "It still wasn't any of his buisness if me and that little crap got along. That brat doesn't know what happened between me and him."