Frankly, even if the Bible/Scripture is your guide for both faith and practice, the issue of single Christian men and single Christian women living together under the same roof (or as the IRS used to categorize such folks, POSSLQs--persons of the opposite sex sharing living quarters) is not in the Bible, at least not in the one I read.
Does that mean single Christian men and single Christian women of virtually any stripe are free to live together--chastely, of course--prior to marriage? Not necessarily.
Christians, generally, look to the Bible for guiding principles in how to live their lives, not hard and fast rules which cover each and every contingency in life. Those who attempt to do the latter are in danger of becoming Pharisaical legalists, whereas those who do the former are on safer ground, particularly if they have developed a sensitivity to the nudgings of the Holy Spirit as he brings particular guiding principles to bear on their unique life situations.
When these nudgings occur (and more importantly when we listen to and obey them) we begin to develop some spiritual muscles, which means, in part, we become increasingly aware of and sensitive to not only what is "right" and what is "wrong," but also what is "wise" and what is "foolish," and what is the loving thing to do and the unloving thing to do.
Paul covers this latter category (viz., loving and unloving) quite well in his letter to the Roman Christians, where in chapters 15 and 16 Paul deals with what could be called "principles of conscience" or "grey issues." In those chapters, Paul encourages mature, strong Christians to be willing to give up a behavior they have the personal freedom to engage in, for the sake of other Christians who would stumble if they knew their fellow Christians engaged in that particular behavior, whatever it might be.
Paul sums up the concept in the following way. Do keep in mind, however, that the issues of conscience in his day were 1) food sacrificed to idols, which some Christians had liberty to eat but others did not; and 2) "special days" in the church calendar, which some Christians felt obligated to observe, but which other believers considered strictly "optional."
I know and am convinced in the Lord Jesus that nothing is unclean in itself; but to him who thinks anything to be unclean, to him it is unclean. For if because of food [or a "special" day] your brother is hurt, you are no longer walking according to love. Do not destroy with your food [or with your observance or non-observance of a special day]him for whom Christ died. Therefore do not let what is for you a good thing be spoken of as evil, for the kingdom of God is not [a matter of] eating and drinking [or special days], but righteousness and peace and joy in the Holy Spirit (Romans 15:14-17 NASB Updated).
All the foregoing to say, the primary question a Christian should ask him- or herself is this: How will my behavior affect others either inside or outside the church, whether they are fellow believers or even non-Christ followers, since even the latter are sometimes watching our every move, looking for inconsistency and hypocrisy?
Keep in mind, our consciences alone cannot be our guide, but only consciences informed and sensitized by the principles of God's word. I have observed over my many years of being a Christian, however, that even having a solid foundation in God's word does not keep us--myself included--from rationalizing virtually any behavior we might care to name. That is one reason why Christians need to live in community with other Christians and interact with fellow believers of all different stages of maturity in Christ.
In other words, we need to be accountable to one another and not be "Lone Ranger Christians," indifferent to how our behavior affects others.
In conclusion, perhaps a parable might be helpful regarding the issue of whether or not to live together with another Christian prior to marrying him or her.
In the days when well-to-do people could afford to be chauffeured around in a horse and buggy, they would hire a man (sorry, ladies) to do the "driving" for them. The driver might even become a fulltime employee of the wealthy person.
One day, just such a wealthy man was in need of a driver, so he put an ad in the local newspaper which read simply, "CARRIAGE DRIVER WANTED IMMEDIATELY. MUST MEET CERTAIN QUALIFICATIONS AND PERFORM A TEST RUN IN ORDER TO QUALIFY FOR EMPLOYMENT."
The ad was successful, and it attracted numerous applicants. After vetting each applicant's qualifications and references, the employer had narrowed down the field to just two applicants. He then told the first applicant to prepare for a test run. After giving him directions for the run, he stepped into the carriage and tried to relax.
Well, the first driver took off like a shot and drove the horse as if he were trying to win the Kentucky Derby. When he came to an extreme curve in the road, which had a very steep cliff on one side, he expertly steered the buggy mere inches from the dangerous precipice and arrived home in record time.
The employer then gave the second applicant the same instructions and again got into the cab and tried to relax, which was no mean feat at this point! The driver took off slowly and gently, giving the horse an easy time of it. At the same extreme curve in the road, this driver stayed several feet away from the precipice and arrived home safely, albeit in something less than record time.
The moral of the story: Who do you think got the job?