The following passage defines what an "unbeliever" is, Biblically speaking:
2 Corinthians 4:3-4 (LEB) But if indeed our gospel is veiled, it is veiled among those who are perishing, among whom the god of this age has blinded the minds of the unbelievers, so that they would not see the light of the gospel of the glory of Christ, who is the image of God.
Notice what it says. unbelievers
would NOT see the light, they are blinded, veiled and are perishing. The Bible never, not once, describes an unbeliever as someone who "believes for awhile then stops believing". God's Word says an unbeliever is veiled, blinded to the Gospel and would not see the light. I believe what it says.
What you say below, describes an exbeliever, not an unbeliever. I presented the Biblical evidence for my view (2 Cor 4:3-4, above) that shows an "unbeliver" has been blinded by the god of this world and veiled from even seeing the Gospel, much less believing it.
It is my observation that no passage in the Bible uses the word "unbeliever" to describe someone that once believed but no longer believes.
And that it is therefore, literally/techically/logically unbiblical to claim an unbeliever, once believed.
I disagree with your statement above, and respecfully request that you provide a Scripture to back up your claim quoted above. Post a passage that describes a person that believes for awhile then calls that person an "unbeliever", please.
https://www.biblegateway.com/quicksearch/?search=Unbeliever&version=LEB;KJV;NKJV&searchtype=all