I know this is on the baseball board, but I can understand it as someone who spent a lot of their adolescence in a state that only had the Cowboys. State pride and all, I rooted for the Cowboys, then the Texans were forced into my life. Thankfully, my disdain for Jerrah compounded with BoB's incompetence has further diminished my interest in both teams in Texas & the NFL's inconsistent enforcement of their policies has seen my overall interest in the NFL wane.
I grew up near the Houston area going to Astros games, but my grandparents lived in FW and took me to a lot of Rangers games during the Pudge/Juan Gone era. While they were in different leagues, I was an Astros fan that followed and wanted success for the Rangers. Since we've combined leagues and suffered the success of the Rangers with millions of lifelong fans suddenly appearing (I know, it happened for the Astros too once they found success, this is just my cursory observation), my affinity for the metroplex team has also seen a plummet, and it largely coincided with my interest in the Astros gaining.
All that said, I could see how it's possible, but not as a diehard for either team.