Living in obedience to God and the laws of the land is the right thing to do.
It is true that a marriage license was developed as a law of the land for two people who choose to live together, and Romans 13:2 reads, "So those who refuse to obey the laws of the land are refusing to obey God, and punishment will follow."
On a more personal note, I am a woman who lived with a man for quite some time. During that time, I sought out God and longed to be closer to Him. To be closer to God, you worship Him and show your love for Him by obeying Him. I realized I was not obeying God so long as I was living with someone without a marriage license, so I prayed about the situation, and the opportunity then became available for us to obtain the marriage license and by doing so we were then living in obedience to man's laws, which meant we were also living in obedience to God's laws.
After I prayed about the situation, the man I was living with suddenly wanted the marriage license as much as I did, and everything fell into place. The finances, the church, the preacher, all became readily available. The marriage ceremony was a pleasant one that took little preparation, and now I feel as though a weight has been lifted off from me.
The reason why you are having to ask the question as to whether or not it is okay to live with someone without a marriage license is because you are caught in a spiritual battle. As long as you want to hear that it is okay to do so then the Evil One will make sure there is somebody around telling you what you want to hear. The reason why you can't just believe and accept those lies is because deep down, the Holy Spirit is telling you different. Once you give in to the Holy Spirit and live in obedience to God, the guilt and the doubts you are having will all float away and you will be much happier.
Sin and all the pain and trouble that comes along with it is a consequence we live with when we do not obey God. Do you and your loved one a favor: Live in obedience to God by obtaining a marriage license. God gives us these laws because He loves us and doesn't want to see us suffer the consequences from not obeying them. Pray, and tell God that you want to obey Him, and He will help you find the ways that will make it easier for you to do so.