And I know them other girls seem pretty
But when you do it big, there are just so... many
He understands that she may get jealous because the girls that are available for him to talk to/pursue might seem attractive (but they might not really be).
When you’re successful, there are plenty of girls who want to be with you.
They don’t mean anything to him.
And Many sounds like mini, so that may be a play on the ‘do it big’.
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