I recently had a seminary student ask me if it was a sin to cohabitate. I have not been able to find anything on this subject.
While cohabit sounds like it just means “live together”, both the dictionary and traditional definitions mean to live together in a sexual relationship without being married. This would involve fornication (or adultery if either is married to a third party), which we know is a sin. See for example section 38.6.5 Chastity and Fidelity in the General Handbook: Serving in The Church of Jesus Christ of Latter-day Saints and the Chastity entry of Topics and Questions on the Church website.
I’m going to assume both you and the student know that the above is sin. I’m also going to assume your student is not asking about having a same-sex roommate (something BYU housing is designed for, for example). This obviously is not sinful. (Though if the issue of same-sex attraction is involved, then please consider that in light of the principles below.)
Another possibility is that the student was asking whether two people of different sexes who are not romantically involved in any way can cohabit without committing sin. My answer to this is basically the same as my answer to the next possibility with the addition that it is only slightly less dangerous.
The final possibility is that the student is asking whether it’s a sin for two people who are attracted to one another (or even dating) to live together so long as they aren’t engaging in sex or other behaviors contrary to the law of chastity. I expect you know both the answer, but you don’t know how to “prove” it. So let’s go with principles instead and let the Spirit speak to both you and the student.
Matthew 5:28 reads:
But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
There is a principle here beyond the literal words – a principle found throughout this chapter: Don’t just avoid sins that involve action, avoid even the thought of sin, or thoughts that lead to sinful actions. A similar principle is taught in D&C 59:6:
6 Thou shalt love thy neighbor as thyself. Thou shalt not steal; neither commit adultery, nor kill, nor do anything like unto it.
In essence, the Lord is telling us to use our brains, recognize that one thing leads to another, and avoid the entire path of sin. Now I can imagine a teen saying, “well, I can live with this other person without lusting after them.” To which I say, “my eye” (I don’t believe it). Living together, even just as “roommates” with separate bedrooms is an intimate thing. The temptations are guaranteed to come eventually. In Matthew 6:14 (JST) the Lord, teaching his disciples how to pray, says:
And suffer us not to be led into temptation…
Do you pull up the pornography site on your phone, and only then pray for God to help you avoid pornography? Do you light up the joint and then ask God to help you not to get addicted? The Lord tells us to pray for help to not be led into temptation. We can only sincerely do that if we have not deliberately or willfully put ourselves in temptation’s path.
In the vision of the Tree of Life, the angel tells Nephi:
17 And the mists of darkness are the temptations of the devil, which blindeth the eyes, and hardeneth the hearts of the children of men, and leadeth them away into broad roads, that they perish and are lost.
To cohabit with a member of the opposite sex is to invite the mists of darkness – to blind your own eyes.
This brings us to the question of what is sin. Your student’s question approaches sin as if there were a list of what is and isn’t acceptable and as long as it’s not on the list, you’re free and clear. Though a common idea for young people, this is the wrong approach. As King Benjamin taught:
29 And finally, I cannot tell you all the things whereby ye may commit sin; for there are divers ways and means, even so many that I cannot number them.
Rather, one should approach the question looking for principles. In Approaching Zion (Chapter 3 “Zeal Without Knowledge”), Hugh Nibley gives a definition of sin that I have liked from the moment I first read it, though it’s brutal in that it leaves no room for doubt or escape:
Sin is waste. It is doing one thing when you should be doing other and better things for which you have the capacity. Hence, there are no innocent, idle thoughts. That is why even the righteous must repent, constantly and progressively, since all fall short of their capacity and calling.
D&C 88:21-22 says this differently, and yet it’s basically the same idea:
21 And they who are not sanctified through the law which I have given unto you, even the law of Christ, must inherit another kingdom, even that of a terrestrial kingdom, or that of a telestial kingdom.
22 For he who is not able to abide the law of a celestial kingdom cannot abide a celestial glory.
In essence, sin is anything less than living the celestial law. Now we may not know and understand all celestial law right now, but we have more than enough to go by and any who progress beyond what we have will surely be given more (see D&C 59:4 & D&C 71:4-6).
So, do you think unmarried people of opposite sexes cohabit in the Celestial Kingdom? I think not. Either they are sealed as husband and wife, or they remain separate and single (see D&C 131:1-4 and D&C 132:15-17).
If more study is needed, I recommend the resources the Church has already provided on its website. Here are a few:
For the Strength of Youth: A Guide for Making Choices (particularly the “Your body is sacred” portion)
“Good, Better, Best” by Elder Dallin H. Oaks, October 2007 General Conference
I hope this helps you and your student understand how to approach questions like this.