...what does matter is what the Bible says.
Please remember that the responses to the question are from a Biblical perspective and not a human opinion. Anything that is stated here should be confirmed for accuracy.
How can I know if I have committed the unpardonable sin?
Matthew 12:31 "Therefore I say to you, every sin and blasphemy will be forgiven men, but the blasphemy against the Spirit will not be forgiven men."
BLASPHEMY — the act of cursing, slandering, reviling or showing contempt or lack of reverence for God. (from Nelson's Illustrated Bible Dictionary)
When we sin, the Holy Spirit convicts us of our sin. John 16:8 "and when He has come, He will convict the world of sin, of righteousness, and of judgment." To convict is to make aware. The Holy Spirit is the one that makes us aware that something is wrong (some people call that our conscience). If we do not yield to the promptings of the Holy Spirit (or listen when the Spirit tells us something is wrong) and seek forgiveness, we have hardened our hearts and we no longer hear. At some point, we then run the risk of not listening at all. If that happens, if we stop listening all together, we have committed the unpardonable sin because we have blasphemed or completely turned away the Holy Spirit.
If you are concerned that you have committed the unpardonable sin, you haven't. The feeling of concern indicates that you are still listening to the Holy Spirit. At this point, it is time to look to God's Word for encouragement and guidance. 1 John 1:9 "If we confess our sins, He is faithful and just to forgive us our sins and cleanse us from all unrighteousness." Look to God's Word for help: John 17:17 "Sanctify them by Your Truth, Your Word is Truth."