Is living with person of opposite sex a mortal sin?

Living with a person of the opposite sex is not inherently a mortal sin, as it depends on the circumstances and the nature of the relationship. For example, cohabitation without a committed relationship or outside of marriage may be viewed negatively in many religious contexts. However, if the living arrangement is platonic or within the bounds of marriage, it may not be considered sinful. Ultimately, interpretations can vary widely based on individual beliefs and religious teachings.