Do we need a ceremony to be married?

The scenario behind this question is that this couple is living together like a married couple without officially being married. The male in the relationship wants to know what exactly is sexual sin and what does the bible say about marriage.

Here is a paraphrase of the question …

Please make us understand what is exactly a sexual sin, I have been staying with my partner for a year now, both our parents know about our relationship. We make love and do everything that people that have a marriage certificate do. We are not at all in a hurry to get married as we are still finding our feet and building our business, our priorities just don’t include the celebration day of our union yet, we will eventually but it’s just not on the top of the list. We are not at all sin conscious, nor do we make room for the law and condemnation in our relationship. We involve God in everything we do and go to church every Sunday. We listen to your teachings and other pastors that we discern the anointing of God over them. Please share your view of marriage Biblically.

1 Corinthians 7:1-3,8-9 KJV

[1] Now concerning the things whereof ye wrote unto me: It is good for a man not to touch a woman.
[2] Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband.
[3] Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband.
[8] I say therefore to the unmarried and widows, It is good for them if they abide even as I.
[9] But if they cannot contain, let them marry: for it is better to marry than to burn.

Genesis 2:21-25 KJV

[21] And the Lord God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof;
[22] And the rib, which the Lord God had taken from man, made he a woman, and brought her unto the man.
[23] And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man.
[24] Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh.
[25] And they were both naked, the man and his wife, and were not ashamed.

Genesis 1:2-3 KJV

[2] And the earth was without form, and void; and darkness was upon the face of the deep. And the Spirit of God moved upon the face of the waters.
[3] And God said, Let there be light: and there was light.

Romans 10:10 KJV

[10] For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.

Genesis 9:1-13 KJV

[1] And God blessed Noah and his sons, and said unto them, Be fruitful, and multiply, and replenish the earth.
[2] And the fear of you and the dread of you shall be upon every beast of the earth, and upon every fowl of the air, upon all that moveth upon the earth, and upon all the fishes of the sea; into your hand are they delivered.
[3] Every moving thing that liveth shall be meat for you; even as the green herb have I given you all things.
[4] But flesh with the life thereof, which is the blood thereof, shall ye not eat.
[5] And surely your blood of your lives will I require; at the hand of every beast will I require it, and at the hand of man; at the hand of every man’s brother will I require the life of man.
[6] Whoso sheddeth man’s blood, by man shall his blood be shed: for in the image of God made he man.
[7] And you, be ye fruitful, and multiply; bring forth abundantly in the earth, and multiply therein.
[8] And God spake unto Noah, and to his sons with him, saying,
[9] And I, behold, I establish my covenant with you, and with your seed after you;
[10] And with every living creature that is with you, of the fowl, of the cattle, and of every beast of the earth with you; from all that go out of the ark, to every beast of the earth.
[11] And I will establish my covenant with you; neither shall all flesh be cut off any more by the waters of a flood; neither shall there any more be a flood to destroy the earth.
[12] And God said, This is the token of the covenant which I make between me and you and every living creature that is with you, for perpetual generations:
[13] I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.

1 Corinthians 14:33 KJV

[33] For God is not the author of confusion, but of peace, as in all churches of the saints.

Matthew 18:16 KJV

[16] But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established.

Ruth 4:9-12 KJV

[9] And Boaz said unto the elders, and unto all the people, Ye are witnesses this day, that I have bought all that was Elimelech’s, and all that was Chilion’s and Mahlon’s, of the hand of Naomi.
[10] Moreover Ruth the Moabitess, the wife of Mahlon, have I purchased to be my wife, to raise up the name of the dead upon his inheritance, that the name of the dead be not cut off from among his brethren, and from the gate of his place: ye are witnesses this day.
[11] And all the people that were in the gate, and the elders, said, We are witnesses. The Lord make the woman that is come into thine house like Rachel and like Leah, which two did build the house of Israel: and do thou worthily in Ephratah, and be famous in Bethlehem:
[12] And let thy house be like the house of Pharez, whom Tamar bare unto Judah, of the seed which the Lord shall give thee of this young woman.