Quick Transmigration, Male/Male, Bad Ending, No Splitting, Mind-Bending, Later Worlds Are Hard to Follow

I can't find that book!!! In one of the smaller worlds, the male lead is an evil Demon Lord who gets captured by the world's male lead. The latter's whole family was killed by the Demon Lord, but there's a misunderstanding. The Demon Lord is awaiting execution, and meanwhile the younger male lead keeps having nightmares about the male lead's past. Bad ending.