What’s the secret to a longlasting, happy marriage? It’s a question that people have asked and debated for centuries and the source of hundreds of self-help books pored over by couples in search of answers. But none addresses the issues in as pointed and straightforward a manner as Sharon O’Neill’s A Short Guide to a Happy Marriage. O’Neill, a practicing family therapist for more than two decades, has always been obsessed with how and why relationships last.