l don't think he'll get caught up over something like that.
Believe it or not, there are a LOT of people who end up as couples but first knew the other person when they were younger. Heck, my best friend is 15 years older then his wife. They met when she was in high school but there was no foul play. And then a few years after she graduated, they started dating and all these years later, they have a beautiful home and four children, one already in college.
I'll say in Heechul's defense, maybe he met Momo when she was a trainee, gave her a couple of pointers, had typical conversations with her, and then years later, they reconnected, somehow fell for each other... and then broke up!
R.I.P. to all those users that were saying things like "I wish them eternal happiness, blah, blah blah" like they were getting married or something LOL.