split the blanket

It mattered to no one that he already had a wife, a white woman named Eliza Allen: they'd split the blanket and dwelt apart, and among the Indians, the Indian marriage took, though not for life nor even long.

"Well, I reckon that splits the blanket," said Will. "Now he knows we ain't buyin' his shakedown, I reckon he'll loose them pet Comanches on us."