How do Catholics reconcile a metaphorical Adam and Eve with Original Sin

It is known that many Catholics believe that Adam and Eve is a story better left to the metaphorical imagination, rather than literal interpretation (though other denominations may feel differently). Going off of this belief, wouldn't that imply that since it is just a metaphor, and not literal, that it never really happened, and if it never really happened, then there is no REAL original sin? If it is a metaphor and there is no original sin, then why did Jesus come to earth? Why did he have to repent us of this non-existent sin?