In "In a Field of Stray Caterpillars," what does David point to as the beginning of the breakdown in his relationship with Tabitha?

David brought Tabitha onto the reservation for a Social dance. Tabitha is white, but she shows a lot of interest in David's culture, and on this night she was excited and curious. But his mother's friend, Cheryl, ignored Tabitha and told David that he should get himself a Native girlfriend, and this lack of acceptance of Tabitha poisoned the relationship a bit for David.