Joe pimping out his 'wife' means she isn't much to him
I am not sure even a hardcore gangster would pimp out his wife. Joe was a desperate man. He and his crew got stiffed. His boat deal fell through. He wanted to retire. Outwardly he said she would ditch the young guy when she was ready. But he had already written her off when he told her to "suit up" and she went along with it. She was just a means to an end. He gave her up for the gold and a comfortable retirement.
If I ever see Mamet, the first thing I would ask him is the ending.