I think it's simpler than all that. When we're younger, we're more easily controlled, more likely to avoid conflict and more likely to want to please our partner. As we get older, we get more confident and we start to speak up. Also, when you date someone the relationship is far different than when you live with someone. Anyone who is married will attest that first year is hard, learning to live with someone and having to set boundaries is hard. I think Brian was a controlling force in Gabby's life and as she matured she began to have her own voice, her own dreams. That frightened Brian, who felt that as losing control, and so the tension built. Add a cross country trip, close quarters and not being able to have anyone around to diffuse the situation and it all blew up.