I've been thinking which relationship resulted in the bigger fiasco.
YoonA and LSG acting like they like each other a lot since 2007/2008 and the following years, YoonA having convinced those close to her that she may have fallen in love with him, which prompts LSG to ask about her to Leeteuk, things happen. They finally start dating in 2013, she claims she always thought he was doing it for the broadcast and how he never portrayed direct interest.
They break up after a year give or take (definitely not 1 year and 9 months lol). 2-3 years later she releases a song a month before his discharge claiming she didn't know his heart then, she didn't know it was love and how it looked like.
That makes absolutely no sense and of course if it turns out that she was/is with someone else, for example Donghae, we'll know she was just speaking bs as on other occasions.
(ALL the truth will inevitably come out sooner or later.)
Or SHK & SJK falling in love through their drama, getting married super pronto, only to drift away from each other after a year and SJK filing for divorce, with the possibility of someone having cheated.
You may choose the second one since there's a marriage and divorce involved, so the mess is on a much bigger scale, and I condensed it but I'm sure there was a lot going on there as well, but on an emotional level, and for all the people involved, I think nothing will top YoonGi's mess. The fact that it's still going on to this day speaks volumes of it.
While of SJK/SHK you'll probably won't hear about them as a couple much longer after the divorce is finalized.
If you think about it, YoonGi are like the mini Song/Song. Netizens like to bring up SHK's past relationships, now more than ever. YoonA only had one public relationship but you'd be naive to think she only dated LSG in her 30 years of life, thus people bring up her rumored ex's from time to time.