A baseball fan’s hopes can be dashed with a swing, and that was exactly what happened to a pensive Yankee Stadium crowd last week when the Red Sox’s Alex Bregman, historically a Yankee killer, calmly pulled a split fastball into left field. His double brought home a valuable ninth-inning insurance run in a crucial postseason game—a scene familiar to Bronx Bombers fans, whose hearts had been broken by Bregman in three American League Championship Series in the last decade.This wasn’t only a depressing scene for New Yorkers: It was also a bitter reminder, to any Astros fans who might have been watching, of what once was and what could have been. Before becoming an All-Star in Boston this year, Bregman had spent his last nine…