Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men. —Matthew 12:31
If you are worried that you may have committed the unforgivable sin, I can assure you that you haven't. Once a person has committed the unforgivable sin, they are not worried about it at all.
The unforgiveable sin is the continued rejection of the Holy Spirit.
When you sin, God's Spirit strives with you, convicting you of that sin. We often call it the voice of conscience. When we heed Him, confess our sins, and turn from them, "He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (1 John 1:9). But God said His Spirit would not always strive with men. There can come a time in a person's life when they no longer hear the convicting voice of the Holy Spirit.
The rejection of the Spirit's witness to your heart—that Jesus is the Messiah, that He died for your sin, and that He rose again—is the beginning of the path that leads to the unpardonable sin. The continued rejection of Jesus Christ as your Savior will ultimately bring you to the place where He will cease to strive with you and you cannot believe. And if you die rejecting Jesus Christ as your Savior, there is no forgiveness, neither in this world nor in the world to come.
Father, there are people in our lives who have been saying "no" over and over —those whose love for darkness exceeds their love for the light. But You love them in spite of their rebellion. May they hear and respond to Your Spirit before they go too far. Amen.