Why does my ex boyfriend always stare at me?

So anywhere I go.. he always stares at me!

At parties. For instance everyone tells me how he checks me out and everything. This one time he was on a balcony starring at me for like ten minutes. But he's the one who ended it, because he chose his other ex over me. But he's not with his ex anymore. and I ain't sure what even happened with that. But I just saw him today, riding his bike while I was driving, and he went passed, and was starring, and even turned his head back to see where I was going or something. But why would you always stare at your ex, when you see them, and yet your the one who broke up with them? Esp, when I just ignore him and never look at him.
Why does my ex boyfriend always stare at me?
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