The only sin that is unforgivable is if you deliberately challenged (blasphemed) the Holy Spirit who is supposed to convict you of your sin. In other words if the Holy Spirit can no longer convict you of your sin, who or what else will?
If you worry about unforgivable sin, then most likely you are not there. Not yet. Hearts with settled hardness against Jesus and his Spirit don’t go around worrying about it. -- David Mathis (desiringGod)
The Holy Spirit will convict the world concerning sin and righteousness and judgment -- John 16:8 (ESV)
If you feel convicted then the Holy Spirit is still working on you and have not yet abandoned you.
"But I am a very bad person!" you might say...
If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness. -- 1 John 1:9 (ESV)
- Have you blasphemed the Lord? -- The Lord will still have grace! (Mark 3:28)
- Did you swear a vow before God (marriage vows, courtroom vows, secret organization vows, etc.) that you regret? -- You High Priest, Jesus Christ will set you free! (Leviticus 5:4-10)
- Did you deny the Lord in public? -- The Lord will still have grace! (John 21:15)
- Did you abort your own baby or murdered a person? -- The Lord will still forgive you! (2 Samuel 12:9,13, Psalm 51)
- Are you a prostitute? -- The Lord can set you free! (Matthew 21:31, John 8:6-11)
- Are you currently a criminal? -- The Lord will still forgive you! (Luke 23:39-43)
- Are you practising witchcraft or the occult? -- The Lord is stronger! (Acts 8:6-24)
- Did you persecute God's children? -- The Lord will still have grace! (Acts 8-9)
All of the above is wrong, but no matter who you are and what you had done, there is hope.