Why is he so nice all of a sudden?

This guy was really mean to me years ago and didn't like me 3 years back. I sat by him once a long time ago and he got up. He couldn't stand me for anything.

Recently he's constantly staring at me and eavesdropping every time im talking to any guy. He's so nice and respectful to me and won't flirt with any girls in my face.

Why is he so nice all of a sudden?
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