My dear friend be careful with how you handle the word of God and the claims you make especially on such an issue as this. Do you realize how heavy language Jesus and the apostles used in regard to this matter? If a person is willing to continue on in sin "because they think they'll be forgiven" - this person needs to examine themselves to see if they are truly saved or not. Consider what the word of God says:
(2 Corinthians 6:14) Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness?
(Matthew 5:28-29) Jesus said, "I say to you that whoever looks at a woman to lust for her has already committed adultery with her in his heart. If your right eye causes you to sin, pluck it out and cast it from you; for it is more profitable for you that one of your members perish, than for your whole body to be cast into Hell."
(John 5:14) Afterward Jesus found [the leper who was healed] in the temple, and said to him, "See, you have been made well. Sin no more, lest a worse thing come upon you."
(Hebrews 10:26-27) For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins, but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries.
(Hebrews 13:4) Marriage is honorable among all, and the bed undefiled; but fornicators and adulterers God will judge.
(1 Corinthians 6:9-10) Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God.
My friends we are commanded not to be joined with unbelievers. If you are already married then you must do your duty as a husband or wife and love your spouse of course, but if you are single and looking, God has clearly revealed His will for you in this matter. Those who are single - beware. Even just a look with lust God sees as adultery in the heart. How much more wicked then is the act of going physical! If you're planning on doing this and think you'll be okay because "you're forgiven" you might want to think again because even though your parents or your pastor might tell you you're saved no matter what, God declares in His word that if you continue on in sin even after you've known the truth, there will be no sacrifice remaining for you except fiery judgment and condemnation in Hell. Instead of planning on sin and fornication you ought to be cutting off your hands and feet and plucking out your eyes (spiritually speaking). Sexual immorality is such a dangerous and destructive thing that, while the Bible tells us to stand our ground and fight Satan with the armor of God (Ephesians 6), it commands us to FLEE from sexual immorality! Please take heed to the word of God here and stop fooling around. Just because God doesn't immediately exact punishment for sins right after you commit them doesn't mean He'll just sweep it under the rug. The Bible says God will judge those who practice adultery/fornication and that they will not enter the kingdom of Heaven.