Having sex outside of marriage hurts your relationship with God. Since God is the source of life, peace, hope, comfort, security, and power—cutting yourself off from God will bring serious consequences.
Dick Purnell says, "The big downer when you get involved in sexual immorality is the loss of intimacy with God. When you are not connected to the vine of Jesus Christ, the eventuality is you're going to dry out and shrivel up the second you open the door to all the other fleshly desires that are in your soul—the carousing, the violence, the anger, the frustration. All this will start flooding your life, and you'll feel powerless with the onslaught."
If you feel that you've moved far away from God, it's never too late to turn back to Him. He will welcome you into His arms in a heartbeat. He wants the best for you.
"God wants you to live a pure life. Keep yourself from sexual promiscuity. Learn to appreciate and give dignity to your body, not abusing it, as is so common among those who know nothing of God. . . . God hasn't invited us into a disorderly, unkempt life but into something holy and beautiful—as beautiful on the inside as the outside. If you disregard this advice, you're not offending your neighbors; you're rejecting God, who is making you a gift of his Holy Spirit" (1 Thessalonians 4:3-4, 7-8 Msg).