I think it's common to see a young woman as only a victim of circumstances and not as an active participant in her own undoing. That's not victim-bashing, btw, that's taking an objective look at the entire situation. HE wasn't preyed upon by some pervy guy (like some underage high schooler we often read about). She pursued a married man. He responded favorably to that pursuit. They both entered into an affair and it was wrong on both their parts. And they each made a choice to continue said affair for some period of time.
That creates a situation that can be (and in this case was) very dangerous. How many women have you heard uttering some form of, "if my husband cheats I'll find and kill that other woman...." I think it happens more than we want to believe. Well, some of those people (men and women) really will take matters into their own hands if confronted by such a reality. I'm not defending it; it's indefensible. But it can and does happen.
When I read some of the things HE allegedly wrote on her SM (namely Twitter) account, I realized she had been playing with fire, lighting matches, and putting her activities out there publicly. Unfortunately no one interceded to get her on a better path than the destructive one she was on. That's sad. Not uncommon though.
So use this tragic situation of this young woman as a teachable lesson. Not to 'scare' someone, but to educate them on the reality of life. If you (the royal you) are going to screw around with someone who is not single, you are inviting WhoKnowsWhat into your life. You may get your feelings hurt, you may get something worse. It's not fair, but life isn't fair, and the point is to be smart, understand right from wrong, understand why, and develop a guideline for the kind of adult you want to be and the kind of life you want to lead. That to me is one possible "pay it forward" type of outcome that can be utilized from this case.