It may be popular with some of your friends, but for both practical and spiritual reasons I strongly urge you not to go down the road your boyfriend is urging you to take.
On a practical level, the problem with simply living together is that there’s no real commitment, either to each other or to marriage. What’s to keep your boyfriend from deciding he doesn’t want to be tied down, and suddenly casting you aside? Or what’s to keep you from leaving after a minor disagreement (as happens in almost any relationship)? The answer is simple: precisely nothing.
But I also hope you’ll avoid this for spiritual reasons. God gave marriage to us for our happiness and mutual help, and in His eyes it’s a solemn commitment to be faithful to each other, no matter what happens. This is why the Bible commands us to avoid sexual relations outside of marriage. Only then can true love flourish, and only then will your relationship grow stronger over the years. Jesus said, “So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate” (Matthew 19:6).
At the moment, your boyfriend’s suggestion may be very tempting, but it’s filled with uncertainty and great risk, as many have discovered, to their sorrow. Instead, I pray you will put Jesus Christ at the center of your life, and seek His will for your future. God’s way is always best.