I Fell for a human -_Underfell!Sans X Reader_- (lemon)

(SLOW UPDATES AND UNDER EDIT) You are a young adult, around the age of 19. You don't really have a gender but can be called he/she or they You were living with an awesome family when your father turned insane and killed your mom, brother, and two sisters while they were sleeping. You on the other hand were wide awake...