Here is a clip of what he actually said. He said only that he would have to respect the nominee. Apparently the fact that the voters would have chosen the nominee was not enough for him.
He did not say anything about being treated fairly at that time. He added that in a subsequent debate after he came under intense criticism and reversed his initial refusal to commit. Then he later repudiated that, claiming that he was treated unfairly.
So it was a very unloyal performance on his part, yet his supporters now complain that others are not loyal to him now that he’s the GOP nominee. Once again, the world’s smallest violin is playing in the background.
I can find fifty different quotes. Trump certainly said he would support any nominee in a fair primary, period.
I believe that was Obama, as America burned all around him.