I am 21. I am not trying to justify what I am about to tell you, but I was a drug addict. Drugs are a tool of the devil. I am now sober for 5 months. I impulsively cursed (damned) the Holy Spirit and said that its power comes from Satan. Is this unforgivable in God's eyes, even if I could believe in Jesus? Can the blood cover this sin?
I am amazed how many people want God to condemn them. I suppose a person could then feel free not to do right because they couldn't be saved anyway. But the truth is that the view is completely backwards from what the Bible teaches.
"The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance" (II Peter 3:9).
"All" doesn't leave you out of God's desire to see you saved.
""But if a wicked man turns from all his sins which he has committed, keeps all My statutes, and does what is lawful and right, he shall surely live; he shall not die. None of the transgressions which he has committed shall be remembered against him; because of the righteousness which he has done, he shall live. Do I have any pleasure at all that the wicked should die?" says the Lord GOD, "and not that he should turn from his ways and live?"" (Ezekiel 18:21-23).
There is only one thing that keeps us away from God and that is our own sins. "Behold, the LORD'S hand is not shortened, that it cannot save; nor His ear heavy, that it cannot hear. But your iniquities have separated you from your God; and your sins have hidden His face from you, so that He will not hear" (Isaiah 59:1-2). What God wants us to do is give up our sins so that He might welcome us home.
When Jesus warned about blaspheming the Holy Spirit, his point is that when a person goes too far into sin, he might go so far that he no longer desires to return. "And anyone who speaks a word against the Son of Man, it will be forgiven him; but to him who blasphemes against the Holy Spirit, it will not be forgiven" (Luke 12:10). You see, forgiveness is based on repentance. "Repent therefore of this your wickedness, and pray God if perhaps the thought of your heart may be forgiven you" (Acts 8:22). It is the work of the Holy Spirit to convict the world of sin (John 16:8). If you reject Jesus or the Father, the word of God brought by the Holy Spirit is still there to work on your heart and perhaps turn you around. But if you reject the Spirit and His work, then the tools needed to convict and turn you from sin are no longer there. Such a man won't come back -- not because God wouldn't welcome him back, but because he is of the mind to never turn around.
That is not the case with you. You know you did wrong and you are willing to make changes in your life. I know how hard it is to come off of drugs -- I've helped a number of people with the struggles. Five months is an excellent start. Typically it takes at least nine months to a year before a person returns to something that is close to normality (depending on what you were hooked on). And what you must always keep in mind is that you are an addict for life. There is no such thing as trying a drug just one more time -- you'll be hooked again and have start over. Nor will the cravings disappear. They will fade, but they have the tendency to pop up at the oddest and most inconvenient times. It can be done. I have friends who have been drug free for many years. I know you can do it as well.
So, quit worrying that God won't forgive you. Put your trust in Him and accept the fact that He is offering to forgive you if you will just be obedient to His will. If I can help in these matters, please let me know.