Why shouldn't couples cohabitate during engagement?

i have a good friend who is dating someone and stated that they will cohabitate once they are engaged. she converted to the faith last year and i was her sponsor. as her sponsor i feel i have an obligation to explain to her that the catholic church frowns upon cohabitation before marriage but i don’t know how to bring it up tactfully and how to explain it. can someone please provide some good suggestions on how to address this issue tactfully and a good answer on why we shouldn’t cohabitate before marriage?

These links should explain to you the Church’s teachings on cohabitation and the sin of scandal. If you have any further questions or concerns that are not answered by these links, please contact Catholic Answers directly.

Recommended Reading:
How do I handle this situation?

Can an unmarried couple sleep together w/out ‘sleeping together’?
Is sharing a bed always a sin?
Why is causing scandal sinful?
Is cohabitation a mortal sin?

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