Is it a sin to live with an unmarried couple?

I was wondering if it is sinful to live with another couple that is not married (in this case they happen to be engaged, although I’m sure that wouldn’t change and inherent wrongness of it).

A favorable living situation has come up that may allow me to live with two friends who are already living together as roommates, but I have moral qualms about the whole situation as I am definitely not in favor of that decision on their part. I am leaning seriously towards not taking the opportunity, although other than that fact it is of much interest to me. Also, if it is a sin, is it grave?

It’s really a matter of prudential judgment; of whether your living in the same home as this couple would signify your approval of their extramarital relationship. If it would, then prudential judgment would caution against it. If for some reason, however, you could not find a comparable living situation elsewhere, you could move in as a short-term solution until you could find a long-term solution.

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