Yes, what your boyfriend has written you is true: It isn't God's will for you to live together outside the vow of marriage.
You see, God gave marriage to us, and He intended for a man and woman to live together only within the commitment of marriage. He did this because He loves us, and He knows that unless a couple is committed to each other in marriage, their relationship will never be completely stable and secure. Down inside your heart, isn't this the kind of stability you yearn for?
Instead of being upset at your boyfriend, I hope you will rejoice that his life now seems to be on a new track. After all, what future would he have otherwise? He'd likely fall back into his old pattern of living and that's a dead-end road. But now that he has come to know Christ, he has a new life. The Bible says, "Just as Christ was raised from the dead through the glory of the Father, we too may live a new life" (Romans 6:4).
And what has happened to him can happen to you! You too need your sins forgiven, and you too need hope for the future. Most of all, you too need Christ and Christ wants to help you. By a simple prayer of faith ask Jesus to come into your life today. Then commit your future to Him, and ask Him to help you and your boyfriend to live in purity as you seek His will for your lives.