Why would a guy like my friends pictures when I liked them while we were dating but stopped when we broke up?

Question pretty much says it, he cheated on me and then we were fighting a lot and not talking during this time anytime I’d like my friends picture (mutual) he’d like it too but then we finally broke up and I deleted him and now he doesn’t like anything of hers.

(we are 19 by the way not 25+)

Updates
+1 y
We broke up by the way when he was trying to fix things because that girl added me on instagram and I asked if they had talked recently and he said no I wasn’t convinced I asked again because why is she requesting me and he didn’t answer so I removed him
Why would a guy like my friends pictures when I liked them while we were dating but stopped when we broke up?
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