I feel really weird idk

So for context my ex and were on and off but we were in a relationship for three years then we broke up (i initiated it) to which he crashed out and saved my pictures and videos and posted all over and I took it down, doxed my number. I had to move on (this was last year November) then this year March we spoke again and he was still mad at me and hurt me, then we cut ties completely. In the month of August he called me on my birthday and from then to now we are in touch, we rarely talk but we kept up on each other’s stuff. Today he posted a picture with another girl on Instagram and I feel a wave of sadness and I don’t know what this is, but I’m anxious and I can’t breathe. I thought I’m healing and I feel much better because I feel such disconnect after all the pain he put me through. I can’t shake off this feeling, he never posted me so he’s now posting someone else, it’s so weird and I can’t stop thinking about it, or comparing myself to her. It’s so weird