Their relationship lasted for half the series, ending when Sally discovered that Don's real passions lay in baking, as opposed to law enforcement, and she whipped him up into a force to be reckoned with, thus taking away the spark they once had.
Their relationship endured for half of the series, concluding when Sally realized Don's true interests were in baking rather than law enforcement. She transformed him into a formidable force, thereby extinguishing the spark they once shared.