Explanation for my ex behaving like this?

So my ex broke up with me nearly 2 months ago. She said she needed space to work on herself. I immediately went into NC.

After, she started behaving psycho and trying to make me jealous with a colleague of mine. She would be cold, then friendly, then cold, friendly, cold, now super friendly

Last time I saw her was Friday, she was play fighting me, teasing me, and seemed as if she got jealous when I was talking teasing another girl.

How I have been behaving? Extremely Happy. I got my career job which she knows about through social media. I am going on a date with a beautiful girl in a couple days (that she doesn't know about), doing fun things with friends,, on top of that, a lot of people like me in our gym. She's been stalking my social media quite excessively through Instagram story.

Thoughts?
Explanation for my ex behaving like this?
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