Happy All the Time by Laurie Colwin

Guido and Vincent are childhood best friends—third cousins, really—living in Cambridge and dreaming about their futures. Guido plans to write poetry while Vincent feels confident he will win a Nobel prize for physics. When Guido spots Holly while exiting a museum, he can immediately sense that she will be difficult, quirky, and hard to live with. He loves her on sight. Vincent, open-minded and cheerful, meets Misty at work. Though she is a bored and misanthropic brunette, he finds himself desperate to know her. Through courtship, jealousy, estrangement, and other perils, Happy All the Time follows four sane, intelligent, and good-intentioned people who manage to find love in spite of themselves.