Why would guy unfollow his girlfriend on Instagram and why would she unfollow him too?

So this is my first post here. I hope some of you will answer. I know guy who used to cheat on his ex girlfriend with his current one. But he didn't end up with her after he broke up with with ex. Instead of her he choosed other girlfriend who is now his ex too. This summer he followed his ex mistress on Instagram but recently he unfollowed her. They even went to vacation. She was following him long time ago before they started their affair but she doesn't follow him anymore either. My friend saw them together on event few days ago so they are still together but according to her they weren't close to each other. Why people do it? He is in his thirties and she is in her twenties.
Why would guy unfollow his girlfriend on Instagram and why would she unfollow him too?
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