adultery is not the "Unforgivable" sin ....
Abraham is covered and has an escape as we read at 1 Corinthians 6:9
"Or do you not know that wrongdoers will not inherit the kingdom of God? Do not be deceived: Neither the sexually immoral nor idolaters nor adulterers nor men who have sex with men
nor thieves nor the greedy nor drunkards nor slanderers nor swindlers will inherit the kingdom of God.
And that is what some of you were. But you were washed, you were sanctified, you were justified in the name of the Lord Jesus Christ and by the Spirit of our God.
"
To be forgiven is to be as if you never sinned in the first place....
So when God says you are clean...its as if in His eyes you were never dirty in the first place...
But....
Abraham was a sinner,,,he sinned...he simply was not really good at a few things and it came back later to be a real problem for him and his Jewish children....(The whole Arab/Jew issue still is something that is always just short of destroying the world).
So we can see that Abraham was forgive by God , and his sins were not held against him....
Yet....
yet the earthly effects of his sin of adultery do still remain as something that even to day, 1000s or years later we are still dealing with and are behind things like the 911 attack etc, etc, etc,,,....