The ML isn't the worst in general but he is the worst for her. Not only would she suffer by being with him and being scrutinized by EVERYONE, he would disrupt the resemblance of balance she has built after her life got ruined by him. Also, this story doesn't show it enough but she was nearly raped and killed because of h and his people, are you telling me that trauma is going to go away and she gets with him and doesn't have those flashbacks everytime him and his people are near her?