The first covenant made to Israel was the Abrahamic covenant and not only was that unconditional, Israel could not have broken it because God was the only One Who made the covenant. That covenant, therefore, was His responsibility only to keep.
So if God will break His promises because fallen men break His law, does that then mean that when those who know Christ as Savior break His law that His promise to save them is cancelled?
The promise earlier given to Abraham's seed, however, is still in effect because Galatians says Christ is the seed to whom the eternal (not conditional) promise was given. Because Christ (not Israel) fulfilled the law completely He has been given an eternal kingdom forever and those who have faith in Him are included.
Where, exactly, in any of the New Testament, does God say that His promises to the nation of Israel are cancelled? How does the fact that Jesus Christ died first for the Jew and then for the Gentile and the fact that He has gathered to Himself a spiritual body from among the Jews and Gentiles translate into God's promises to His covenant nation being cancelled?
Where, exactly, is that Scripture?
No, Galatians says that was to one man and his seed (Christ). It was not to the nation because they did not become a nation until 430 years after the Abrahamic covenent.
So if God will break His promises because fallen men break His law
God didn't break His promise. But men broke the law which came much later.
Where, exactly, in any of the New Testament, does God say that His promises to the nation of Israel are cancelled?
I already told you...they are fulfilled, not cancelled.
Those with faith in Christ's work don't have to worry about breaking the law; it's Christ who fulfilled it all. We have faith in His accomplishment...not our own measley attempts...if we go back to our own attempts we go back to a curse as Paul says in Galatians. Better to just rest in His perfection.