Why do I feel sad and jealous when someone has a “one that got away?” Does everyone have one?

I’ve never been in line or a relationship so it cuts pretty deep that literally everybody I know has one of those
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So I mean when a guy I romantically have feelings for talks about his “one that got away” and how he will always love her.. I feel sad and jealous because it seems he isn’t over here or still has hope for their future and you can’t genuinely want a future with two people at once
Why do I feel sad and jealous when someone has a “one that got away?” Does everyone have one?
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