We know This Is Us loves giving us a twisty surprise, and it loves an episode theme that ties multiple timelines together, and, wow, does it love Cat Stevens. But one of the best This Is Us traditions the show has given us over the years is its Big Three trilogy. In both seasons two and four, This Is Us has bucked its typical format to dedicate one episode to each member of the Big Three, examining that one character in multiple timelines and typically weaving the episodes together by showing us at…