Why would my ex post more pictures of him and his new girlfriend after I said it’s nice to see him happy?

I feel like he’s been doing it to try to get to me, and after I focussed on the positives by saying it’s nice to see him happy he’s been doing it more and posting his own pictures of them rather than just sharing hers. Why might he be doing that?

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Looking for genuine advice from those who’re more mature with well rounded experience. Trolls will be deleted.
Why would my ex post more pictures of him and his new girlfriend after I said it’s nice to see him happy?
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