I recall a line from one of Vonnegut's later novels - "What is more Protean than adultery. Nothing."
Maybe spirituality is more Protean than adultery ... I feel sure of it.
I searched for “protean adultery” just to see if I could nail the source, and the first hits were my own FR posting! Then there was some crazy site loaded with ads and links with the title “KURT VONNEGUT JAILBIRD BY THE SAME AUTHOR PLAYER PIANO THE SIRENS” ... well, I guess that would be THE SIRENS OF TITAN. Anyway, I think JAILBIRD was it, but I don’t see any other mention of it at this site! It’s all getting too weird for me.