Why doesn’t my ex want to be friends?

My ex and I moved from her home on the West Coast to the East Coast to start my residency. During this time, I fell in love with one of my colleagues who is also in the program. I ended things with my ex and began an official relationship with my now girlfriend and things are great. The only thing is, my ex doesn’t want to be friends and avoids us (we are in the same social circle).

She has blocked me on everything and has taken a step back from our friend group. She seems to be doing fine, according to LinkedIn (before she blocked me on there too) she received a promotion at work and will be starting an MBA program in the Fall. On the rare occasion that we are in the same setting, it’s awkward. She’s polite, but gives me the cold shoulder and isn’t particularly engaging with my girlfriend and I. I’ve asked if we could talk multiple times and she keeps refusing.

I don’t understand why we can’t be friends (especially since we have mutual friends).
Why doesn’t my ex want to be friends?
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