Why would he follow me on social media & should I follow him back?

This guy I used to talk to that liked me followed me on TikTok recently. We have history and talked off and on for years. I didn't like him back romantically and he was upset at that. Our last interaction was an argument in which he felt I was playing games and stringing him along. If things ended bad and he knows I don't reciprocate his interest what is the reason for following me?
Why would he follow me on social media & should I follow him back?
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