Dear Jay:

Cohabitation refers to a man and woman living together as if married to each other when they are not married. The technical word for this is "concubinage." Concubinage is a grave sin.

The dictionary definition of cohabit is to "To live together as spouses; to live together in a sexual relationship when not legally married."

For a situation in which a man and woman are living in the same house as brother and sister, as housemates, the word "cohabitation" is thus not the right word. A word like "housemates" is more appropriate.

To live together as brother and sister, that is, in a platonic relationship is not sin in itself, unless doing so causes scandal and such a couple needs to be careful about scandal to others, that is, the impression that they are "living in sin".

Such a couple also needs to be careful about the near occasion of sin between themselves.

For example, the couple should not be sleeping in the same bed, should not present themselves in their underwear in front of each other, and similar behavior. Their demeanor to each other needs to be the same as a standard roommate situation with proper modesty and privacy toward each other. They should be fully dressed in front of each other and not provocative in any way.

God Bless,
Bro. Ignatius Mary