<<<Let's major in the necessity to keep believing until Jesus comes back>>>
As I said, continuing to believe to the end is a given or is part of the nature of true faith.
Therefore, if you should end up not believing to the end, it would be a sign that you never had true faith; no matter if you thought your faith was true up to that point or not.
The point being that if you never had true faith, as evidenced by the fact that you do not continue in the faith, your response should be to place your faith in Jesus for the first time (while you may think that you had faith in Him before, it was not valid because you ceased from faith).
And of course the problem with this theology is that, if you thought that you had faith before and it wasn't genuine, how can you know that your faith is genuine now, if you place your faith in Jesus now?
Only if your faith is a heart faith that is unto righteousness (Romans 10:10) and enduring to the end (Matthew 10:22, Hebrews 3:6, Hebrews 3:14).
But how can you know that it is this kind of faith unless you have already endured to the end...?
Therefore your theology is not conducive to assurance of salvation.
Nevertheless it is written,
1Th 1:5, For our gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance; as ye know what manner of men we were among you for your sake.
Here is how you can have assurance of salvation.
Just know that you are currently abiding in Christ and ask Him to seal you with the Holy Spirit so that you can know that you will continue to abide until the end of your days (1 John 3:22; see also Romans 11:20-22).
If you abide in Christ to the end of your days, you will enter in to the kingdom (Matthew 10:22).
Of course you can know that you have
everlasting life from the moment of first faith (John 5:24 (kjv)).
Nevertheless, there is a kind of faith that will fall away when temptation comes (Luke 8:13).
Is it saving faith? I think that it is. It had the power to save the man from his sins (Matthew 1:21, Titus 2:14) for a season.
It just didn't save him from the ultimate destination of hell.