Why did Mr. Dolphus Raymond's fiancee die? What does this show the reader about life in Maycomb?

His fiancée killed herself after the wedding rehearsal. She used a shotgun pointed at her head and pulled the trigger with her toes. She could not handle the fact that her fiancé had a "colored woman" that he hoped to keep while he was also married. Her main point here seems to be that he had a colored woman rather than a white woman. This speaks to the inherent racism in Maycomb.