It sounds like she’s a commitmentphobe. Men are often labelled that, but women can definitely be that too.
Try reading reviews of a book called “Men who Can’t Love”. Yes it’s about men, but you might see your ex’s behavior there. It might help you.

My ex left me unexpectedly after a year of bliss. I never saw the breakup coming and have been a mess ever since, wondering why, what did I do wrong, etc. It’s been about 2 months since the breakup. I’ve ordered the above book. But even reading the many reviews on A m a z o n have helped a lot. I’m sure now he is a commitmentphobe, also known as a love avoidant (I have books on avoidants too). Knowing they cannot commit because of some inner issue makes it easier because you don’t blame yourself.

Oh and just cuz she married another guy doesn’t mean they will leave happily ever after. If she IS a commitmentphobe, they won’t. But you do have to move on, as everyone has suggested. She won’t change. Hopefully this knowledge will give you peace.