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.

This happened long or shortly before they physically left.

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.

Switch 2 quietly makes shiny hunting in Pokémon Scarlet and Violet way better - Polygon

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.

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.

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

Will my 9 year old face more difficulties than most girls her age if she’s an early bloomer? My daughter already needs regular B cup bras. The doctor says that my daughter will be even more developed by 11-12 years of age.

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.

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.

You both are on polar opposites of the scale.

India to Open Flagship EV Making Policy to Lure Global Giants - Bloomberg

So, don't try to compete with them.

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.