You mean he was lying all along, sort of like that other lawyer from Illinois that was against "gay marriage"?
So does this mean the people in the South were right to not trust him? That they called him out correctly?
Yes, Lincoln started out with "If you like your slavery you can keep your slavery." And of course, just like that other Lawyer from Illinois, that simply meant until he changed his mind.
In 1860, just as in 1788, every American understood that slavery was a precondition for Union.
It was part of the deal, without slavery there would be no Union, and that is why until the mid 1850s there had never been an anti-slavery political party.
Republicans were the first specifically anti-slavery party, but no leading Republican in 1860 imagined that slavery could be abolished by Federal government in states where it already existed.
The Republican platform and goal in 1860 was to limit the expansion of slavery into western territories which didn't want it, or into Northern states via the Supreme Court's Dred-Scott decision.
But once the Deep South declared secession and war on the United States, then everything changed.
Now slavery could become -- just as the Brits had done during the Revolutionary War -- a weapon against the Confederacy.
Every slave freed by the Union Army was one less worker for the Confederacy, and one more potential soldier for the Union.
It was a two-fer, a win-win for the Union.
As for Southerners not trusting Lincoln, they should have trusted him much more to obey the Constitution in the face of their rebellion, insurrection, "domestic violence", invasion and treason.
Then war might be avoided, and slaves freed peacefully.