Fifteen years ago Julie Keyes, an artist, art dealer, art consultant, and real estate agent at Saunders and Associates in Bridgehampton, met Adam Tihany, an internationally renowned interior designer. The introduction, made by Ms. Keyes’s beau, Nathan Slate Joseph, an artist who works out of a barn in Bridgehampton and lives with Ms. Keyes in Sag Harbor and New York, changed her life.