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

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.

This happened long or shortly before they physically left.

Why do men love to stink/being smelly?

So, don't try to compete with them.

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.

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.

How do I maintain and care for granite countertops in a coastal climate like Pompano Beach?

You both are on polar opposites of the scale.

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

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.

Can Donald Trump use the Alien Friends Act of 1798 to give ALL illegal immigrants an ultimatum: You have 1 month to leave America, after which you will be arrested and jailed for 3 years?

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.

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.