She dated Sungmin, right? I remember on IY2 they brought him on for like this family holiday special or something.. They brought in Jiyoung's mom, Yewon's mom, Hyoyeon's friend, Suzy's dad, Bora's brother, and I forgot the rest and for Sunny, they saved her last. She kept asking, "is it my ex-boyfriend?" and Sungmin popped out and she was all like nooooo. Lol I don't know if they were joking or not buuuuuuut it sounded legit from how well they knew each other during one of the games and their fried chicken story.
I have read this a lot of times, and If you see the cut you realized it was not like that, When Sunny said "Did we date?" to guess what person was, you can see its like joking around, and he didnt go out when she said that. Maybe it just me, but I dont have the feeling that she confesed that, here you have the video btw
Anyway, I do think they have dated and actually I think the dated between SM concert on 2012 I guess? and IGAB
From a date next to this:
Until a date after this: