Right, I'll make this abundantly clear.
If you went with another person and knew they had a partner, whether you are young or not, it's foul. We know right from wrong from a young age.
However, yes, there are shades of grey and there's a vast, vast difference between something like this and a person who does and it gives zero fucks about who they hurt in the process.
You being happily married now is irrelevant, although good for you, I'm happy for you.
The saying above refers to the person who done the cheating - ie the person who cheated on their partner, not you, but you were complicit.
It is not your responsibility to readjust someone's moral compas who will willingly hurt someone who they are in a relationship with, but it is your own responsibility to reign in your own actions.
Also, no blame can be placed on a person who had no idea the shithead they were seeing was already in a relationship.
But hey, maybe I'm wrong, fuck those long suffering partners who will have their self esteem ripped to shreds, their homes wrecked and their kids absolutely destroyed; it was just a fling and it's not the OW fault whatsoever.