I really enjoyed this TED Talk presented by Esther Perel, a relationship therapist who examined why people cheat and how infidelity threatens our emotional security. She explores what we often do not see...both sides of it, and the expressions of loss and longing. This presentation is a must watch for therapists who work with couples, and anyone who has experienced infidelity (as the person who cheated or the person who was cheated on).
I believe that Ms. Perel did an excellent job of creating a relationship framework, especially for such an uncomfortable topic. The was the best "neutral"explanation I have ever heard given by a professional, and I have recommended this presentation for dozens of couples with positive feedback.