My ex moved on so fast. How can I overcome the pain?

Instead, focus on taking care of, solving and healing what you are experiencing right now.

So, don't try to compete with them.

I.e. you thought that you had the perfect deal whereas they had already made up their mind and just weren't as emotionally invested in it as you were.

When North Koreans visit other countries for the Olympics, what stops some of them fleeing away into that host country?

This is why you can't expect them to feel anything close to what you're feeling right now, because you and them are on a completely different stage in the healing process.

You both are on polar opposites of the scale.

This is why comparing yourself to them in terms of the healing process isn't going to help you in any way, shape or form.

What were my 10 favorite great rock albums that were either forgotten or hardly known by the rock community at large during 1965-‘75?

This happened long or shortly before they physically left.

Simply put, because they have been prepared and you weren't.

And during this process, they either started seeing someone new who they planned to secure as their rebound option or were busy creating their post-breakup plan.

Is there such a thing as "left wing fascism"? If not, what is an example of a political ideology that is often mistakenly labeled as "left wing fascism"?

On their side, there has been a process of emotionally and mentally checking out while you were still together and while you were under the impression that everything is cool.

What they do doesn't matter and it's completely irrelevant to your healing process, though it’s valid to hate and judge them harshly for leaving the way they did.