I honestly think that they two did went put or still went out together. Maybe just maybe Yoona' s relationship with Seunggi is just a stage one because he seems to fit her image well. (I have nothing against Seunggi because I like him). Or Taecyeon and Yoona did have a relationship back then because see how flustered Yoona was and how honest Taec looks because we all know how silly Taecyeon is, actually. Peace all