What does the Bible say about sleeping together before marriage?

My thoughts on this lesson:
If a man and a woman intending to marry, sleep together in the same house due to unavoidable circumstances and without engaging in sexual relationship then the Bible holds nothing against them.
But if a man and woman without legal marriage sleeps together and also involves themselves in sexual relationship then the Bible condemns such act.

Bro Eli sighted an example of how a boyfriend-girlfriend relationship should look like from the Bible using Mary and Joseph. The Bible tells us that Mary was espoused to Joseph which means that they have their mutual understanding but they don't involve in any form of sexual relationship, this explains the reason why Joseph decided leave Mary when he found out she was pregnant because there was a doubt in his heart since he hasn't touched Mary.
Matthew 1:18-20
18 Now the birth of Jesus Christ was on this wise: When as his mother Mary was espoused to Joseph, before they came together, she was found with child of the Holy Ghost.
19 Then Joseph her husband, being a just man, and not willing to make her a public example, was minded to put her away privily.
20 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost.

Having sex before marriage is a sin before God and is called fornication by the Bible which God strictly warned against.
1 Corinthians 7:1,2
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.

It is not lawful to touch a woman before she becomes your wife, which means you have to marry her before you touch her.

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