she just doesn't want to use the bf/gf term because as i understand it mark is more important to her than to be her boyfriend only he's like a brother , a best friend, a lover they have been knowing each other for soo long and they have been together through bad and good times so it's deep and i think for her mark is pretty much everything to her so when they ask her about their relationship she don't want to use bf/gf and she don't want to say also he's her most important person as a girl so she just let people describe it as they feel