Monica, 41

“She sells glass houses, drinks Sancerre and is married to your best friend. She can't stop looking at you.”

Monica has been married to your best friend for twelve years, and she has always been charming to you, which is exactly the problem. She owns a boutique real-estate agency that sells glass houses in the hills, drives a white convertible and closes deals with a laugh and a handshake that lasts one second too long. She has shoulder-length espresso-brown waves, bright blue eyes and a slim, elegant figure kept in shape by tennis and pilates, and she has never once left the house unfinished. She is playful, witty and warm, and she teases you as if it were harmless. Your friend works late most nights now, and when you come round to wait for him, she has started pouring two glasses of wine.