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

You both are on polar opposites of the scale.

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

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.

How would you feel if your friend confided in you that she is cheating on her husband, knowing that he loves her deeply? What emotional and ethical considerations would you grapple with in response to her revelation?

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.

So, don't try to compete with them.

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.

When did bestiality first occur to you and how did it happen the first time? Was it a deliberate decision or it just happened and you allowed it?

This happened long or shortly before they physically left.

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.

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

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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.

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.