How the betrayer can rebuild the trust
Take complete responsibility for your actions. No matter how driven you felt to have the affair, nobody made you do it. The more you blame your partner, the longer it will take him or her to believe that you are trustworthy and want to forgive you.
Assume it will take time for your partner to heal. Your feelings of guilt, shame, or humiliation may cause you to be reluctant to raise the topic of the affair or, when raised, cause you to close down the conversation prematurely. Don't. Assume that it will take at least a year for your partner to be able to trust you again. You should be prepared to maintain an on-going, sometimes painful conversation about your betrayal.
Be empathic. Your guilt and shame may make you uncomfortable listening to how badly you've made your partner feel. However, it is critical that you show empathy and make amends for how much hurt you caused your partner. Showing that you are willing to bear your feelings of guilt, remorse, or fear of losing your partner without blaming back or cutting off the conversation will go a long way to proving that you are someone worth trusting again.
Respect the need for new limits or rules. Your partner has good reasons to be more suspicious than he or she was prior to the event. Accept that there should now be more transparency around emails, phone logs, etc. The less defensive you are, the more quickly will your relationship heal and trust get re-established.
Show an enthusiasm for change and repair. Your partner may doubt that you want to change. If you really want show that you are worth trusting, you will have to demonstrate that you are in it for the long haul. This might mean changing jobs or moving out of the area where you live.
How the betrayed person can rebuild trust
Avoid humiliating your partner. It will be tempting to watch your partner squirm at the end of a hook for making you suffer. However, at some point you have to decide whether you want revenge or a relationship. You can't have both-at least not for very long. If you fail to allow your partner to make sincere amends, there's a greater chance your relationship will end.
Take responsibility: While one person can't cause another to have an affair, sometimes people become more tempted because they feel so rejected, hurt, or starved for attention. The more you can take responsibility for whatever role you might have played, the more quickly will the relationship heal
Separate out complaints from criticism. Your relationship will heal more quickly if you communicate your complaints in a way that makes your partner motivated to continue to want to re-establish trust. Shame, humiliation, and criticism are counter-productive because they cause the other to shut down, avoid, and retreat.
Isolate the times that you talk about the betrayal. It is tempting for a betrayal to become a 24/7 topic of conversation. This can be damaging to both parties. Don't underestimate the power that positive distraction has in creating a happy life and relationship. Agree upon a time to check in on the topic every day for 15-20 minutes. The person who has been betrayed should make the decision about when to reduce the frequency of the conversations.
Write out a list of what would help you feel more trusting. There is nothing more precious to us than our ability to trust our perceptions. You have the right to regain a sense of control, even if it infringes on the usual rules of privacy. After a betrayal, it is legitimate to be able to look at phone records, emails, and cell phone logs in order to feel reassured that there is congruence between what your partner says and does. It may seem radical, but all bets are off after a serious betrayal. I even encourage some of my clients to hire a private investigator if they're truly unsure.
Get help. Most people need to get into individual or couple's therapy to heal from a betrayal and to make a plan for going forward.
Some other interesting background info is the following:
Dr. Coleman Bio:
Dr.Coleman is a frequent guest on the Today Show, NPR, The BBC, and San Francisco's View from the Bay. He has also appeared on ABC 20/20, Good Morning America, America Online Coaches and numerous news programs for FOX, ABC, CNN, and NBC television. He is a psychologist in private practice with offices in San Francisco and Oakland, California and is a Senior Fellow with the Council on Contemporary Families. He has served on the clinical faculties of The University of California at San Francisco, The Wright Institute Graduate School of Psychology, and the San Francisco Psychotherapy Research Group. His advice has been featured in The New York Times, The Chicago Tribune, Psychology Today, The San Francisco Chronicle, Parenting Magazine, Cosmopolitan Magazine, and many others. He is also a contributing editor for Twins Magazine. Dr. Coleman is the author of four books and his books have been translated into Chinese, Croatian, and Korean, and are also available in the U.S., U.K., and throughout Europe.