Mating in Captivity, Esther Perel
On desire in long relationships, and why closeness and eroticism so often pull against each other.
A short, growing list of books, organisations, and helplines I often recommend, useful whether or not we ever work together. These lean UK and international; I tailor them to wherever you're based.
These are starting points I trust; I'll always help you find the right local service for your situation.