What is this feeling?

My ex started dating someone new. I recently checked his ig on his birthday and they were on vacation. It’s been like 6 years and we’ve both moved on. But he also stalked me on my birthday this year. I’m not jealous I think and it doesn’t make me sad or angry, I think I’m happy for him but it just makes me feel a certain type of way? It makes me want to go to the gym but not in a “I’ll show him” type of way. I’m not in love with him anymore but what is this feeling

What is this feeling?
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