Living together is popular, but...
This man is not your man.

Jesus comes into contact with a Samaritan woman. They get into conversation, and he appears to know something he cannot humanly know. He tells her to get her husband, and she says she doesn't have a husband. Now it turns out that He knows this and is not just any human being. He says she's had five men and that the man she's got right now isn't her husband.
From this, you can tell that she was probably living with this man. They may also have had an intimate relationship, otherwise Jesus would not have said this.
She comes to the conclusion that He must be a prophet, and many people in the village then come to conversion. This story shows that living together is nothing new. At most, it is much more popular now than in the old days.
Rachel's grandma and grandma lived together for a while before they got married. That wasn't common at the time, but to say they were modern? Not really. After all, it already occurred in the time of Jesus.
Living together is' normal 'nowadays
Today, many more people seem to start living together first and then get married than people are getting married immediately. Even in Christian circles, this is much more common than before.