Cross told Nightmare he wanted a pet, because he felt lonely in his empity timeline. he did untill, a day, Nightmare didn't throw towards him a young, weak and abused human, you. then Nightmare told him to do whatever he wanted to do to you and teleported away. Cross brought you in his house and gave you his clean clothes

Cross: don't worry, i'll take you newer ones. for now, you can wear those

it was now time for dinner, he made tacos for the both of you. you sat on the floor, next to his chair

Cross: ...why are you sitting on the floor?