May Christians never forget, God hates sexual immorality and will punish the unrepentant:
For this is the will of God, your sanctification: that you abstain from sexual immorality; that each one of you know how to control his own body in holiness and honor, not in the passion of lust like the Gentiles who do not know God; that no one transgress and wrong his brother in this matter, because the Lord is an avenger in all these things, as we told you beforehand and solemnly warned you. For God has not called us for impurity, but in holiness. Therefore whoever disregards this, disregards not man but God, who gives his Holy Spirit to you. (1 Thessalonians 4:3-8)
But I have this against you, that you tolerate that woman Jezebel, who calls herself a prophetess and is teaching and seducing my servants to practice sexual immorality and to eat food sacrificed to idols. I gave her time to repent, but she refuses to repent of her sexual immorality. Behold, I will throw her onto a sickbed, and those who commit adultery with her I will throw into great tribulation, unless they repent of her works, and I will strike her children dead. And all the churches will know that I am he who searches mind and heart, and I will give to each of you according to your works. (Revelation 2:20-23 ESV)
Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolaters, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God.
“Food is meant for the stomach and the stomach for food”—and God will destroy both one and the other. The body is not meant for sexual immorality, but for the Lord, and the Lord for the body.
Do you not know that your bodies are members of Christ? Shall I then take the members of Christ and make them members of a prostitute? Never! Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, “The two will become one flesh.” But he who is joined to the Lord becomes one spirit with him. Flee from sexual immorality. Every other sin a person commits is outside the body, but the sexually immoral person sins against his own body. Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body. (1 Corinthians 6:9-10, 13, 15-20)
But sexual immorality and all impurity or covetousness must not even be named among you, as is proper among saints. Let there be no filthiness nor foolish talk nor crude joking, which are out of place, but instead let there be thanksgiving. For you may be sure of this, that everyone who is sexually immoral or impure, or who is covetous (that is, an idolater), has no inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience. Therefore do not become partners with them; for at one time you were darkness, but now you are light in the Lord. Walk as children of light (Ephesians 5:3-8)
There is no option of living together and getting engaged. God does not suddenly approve of sin because you plan on eventually getting married. In fact, that’s a slap in the face to His holiness and the righteous standards He places upon every believer. This is the only option:
Now concerning the matters about which you wrote: “It is good for a man not to have sexual relations with a woman.” But because of the temptation to sexual immorality, each man should have his own wife and each woman her own husband. Let the husband render to his wife the affection due her, and likewise also the wife to her husband. The wife does not have authority over her own body, but the husband does. And likewise the husband does not have authority over his own body, but the wife does. (1 Corinthians 7:1-4)
Get married, then you can have all the sex you want. Until then, practice your faith by walking in self-control which is a fruit of the Holy Spirit. If you really have Him, you will be able to do all things through Christ who strengthens you, including overcoming sexual sin. If you don’t care, God will judge you as He promised He will, and it won’t be pretty.
God is to be feared, not mocked. And He will reward everyone according to their deeds.
I pray you choose to obey Him and experience His restoration, power, and love like never before.