Rufus stumbles home drunk in part 10 of the story and tells Alice and Dana that they are "only one woman". The following is from page 228:
"Behold the woman" he said. And he looked from one to the other of us. "You really are only one woman. Did you know that?"
After this Alice asks Dana if her and Rufus ever sleep together and she answers no confirming Alice's hunch on what Rufus means. Between the two of them Rufus gets what he wants out of a relationship. He wants to sleep with Alice and talk with Dana. And it helps that the two woman have similar appearances.