Dear Supercryptid,
Our Lord Jesus said all manner of sin shall be forgiven men, except the unforgiveable sin against The Holy Spirit (Matthew 12:31).
As said in some of the above posts, it's important to keep that verse in context of the Messages within the Book of Hebrews. (I'm going to use Paul as the writer of Hebrews in this, though I realize many scholars disagree on that point, and others here may also).
Note Messages like at the end of Hebrews 5 about the "strong meat" vs. the milk. He (I think Paul) was rebuking the Hebrews about not coming to the level of understanding in God's Word they should have been at, since God first gave Israel the "oracles" involving His Plan of Salvation through The Savior Jesus Christ. Those Jews should have understood those Messages about the change to a better Covenant through Christ Jesus, and ready to see its fulfilling right before their eyes, because The Gospel was first written of in the Old Testament they had possession of.
So after the rebuke about the 'milk' understanding vs. the "strong meat" learning, he continues in Hebrews 6...
Heb 6:1-9
1 Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God,
2 Of the doctrine of baptisms, and of laying on of hands, and of resurrection of the dead, and of eternal judgment.
3 And this will we do, if God permit.
4 For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5 And have tasted the good word of God, and the powers of the world to come,
6 If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put Him to an open shame.
At that time in history, the orthodox Jews were vehemently against Christianity and The Gospel. Instead the corrupt Pharisee system ruled over them in the seat of Moses, as the priesthood had become corrupt through the Babylon captivity of the "house of Judah" (hinted at within Ezra and Nehemiah, and histories by the Jewish historian Josephus). That system still sought to be justified by following The Law, religious dogma, animal sacrifices and ceremonial ritual, as it still desires today under the name of Judaism. So that is what those Jews Paul was speaking to came out of, believing on The Savior Jesus Christ. And to fall away from Christ after having come out of that, having been enlightened and tasted of the heavenly gift, then to go back into that old Phariseeism of unbelief would be like crucifying Christ all over again.
Heb.6:7 For the earth which drinketh in the rain that cometh oft upon it, and bringeth forth herbs meet for them by whom it is dressed, receiveth blessing from God:
8 But that which beareth thorns and briers is rejected, and is nigh unto cursing; whose end is to be burned.
9 But, beloved, we are persuaded better things of you, and things that accompany salvation, though we thus speak.
(KJV)
The thorns and briers are symbols for the fruit of the workers of iniquity, those who follow darkness. Those symbols were given by our Lord Jesus in His parable of the sower (Matt.13). Those symbols are linked to the parable of the "bramble" in Judges 9, when the 'trees' (people) finally asked the bramble (symbol of Satan) to be king over them, and the bramble said only if they would trust in his shadow. A bramble thorn bush doesn't cast much of a shadow of protection, so it was all a lie, showing their mistrust and misplaced faith (see also Luke 6:44 about the trees and fruit). So the comparison of good fruit and thorns made in those verses are about God's blessings depending on who and what is followed. The thorns will be burned, thus showing in this what those Jews would be going back into if they fell away from Christ to go back into their old ways of unbelief.
Heb 10:26-30
26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins,
27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries.
That warning Paul gave in the above Hebrews 6 example goes with this one. Note the idea of Christ's adversaries being devoured in God's judgment is mentioned here again. This goes with that idea of falling away from Christ and wanting to come back being like crucifying Christ all over again. So these examples help us to understand better a type of wilfull sin he was talking to them about, which is about unbelief, denying The Savior and the heavenly gift, etc., in order to turn back to the ways of this world among the children of darkness (thorns and briers to be burned in the fire).
Heb.10:28 He that despised Moses' law died without mercy under two or three witnesses:
29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?
30 For we know Him That hath said, "Vengeance belongeth unto Me, I will recompense, saith the Lord." And again, "The Lord shall judge His people."
(KJV)
Those who worked iniquity and wickedness in Old Testament times refused the Old Covenant, and they died without mercy for that. That again shows us the level and type of sin he is talking about. So the question is, have you "trodden under foot the Son of God"? I don't think so, because your words don't show that. Have you counted the blood of the Covenant "an unholy thing"? Again, I don't see that in anything you expressed. Have you done spite unto the Spirit of grace? I would say no, you haven't done that either. And that's the level of willful sin being spoken about there, not little habits we fall into that we have a hard time breaking because of our flesh weakness, while repenting and trying to get back on track in following The LORD.
In Christ Jesus,
Dave