Why is my ex being territorial?

I have a fuck buddy and I posted a pic of us on my snap story and my ex texted me asking about him. Later on my ex asked if we could fuck and I said yes just to see what he’d say. Well he said I had to do favors for him and I asked what he meant. He told me one which idc for but then he said that I have to send a pic of me and him to my fuck buddy after sex. I asked why and he said “To show who’s a bigger man”. Wtf is that supposed to mean? Why does my ex wanna do that? He broke up with me and said he moved on. It’s been a whole year and now he’s acting like this. We’re supposed to be friends.
Why is my ex being territorial?
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