Poor communication likely contributed to the betrayal; one or both of you was not being open and honest. To ensure this is remedied, identify barriers to effective communication and ways to overcome them. This will show your partner you are committed to avoiding future betrayal.  If you or your partner is uncomfortable discussing emotions, agree to write letters to each other about emotional subjects. If you and your partner do not communicate frequently enough, schedule weekly dates to discuss your relationship. If you are struggling to identify why you and your partner are not communicating effectively, consider enlisting the help of a couples counselor. A counselor will be able to help you identify and solve communication problems. You may be at a loss as to how to earn your partner's trust again. Ask your partner what you can do to help them move toward trust. This may mean communicating more regularly, spending more time together, going to counseling, being patient, or something else. Ask your partner to guide your behavior in order to build trust. For example, "What can I do to help you feel more secure in our relationship, and prove my faithfulness from now on?" Contact throughout the day will demonstrate you are thinking about your partner. This will help ease concerns that you are acting without regard for him or her. Your partner is more likely to trust you if they feel connected to you. A good way to maintain contact without being needy is to text funny photos or brief descriptions of funny interactions you have with others. Once you have apologized and made a plan to behave differently, try not to dwell on the hurtful event(s). Refocus attention on the present by engaging in fun activities together. If you are spending more time with your partner, they will worry less about what you are doing when you are apart.  Find a hobby you and your partner can enjoy together. This will increase the amount of time you spend together and can strengthen your bond. Show them how much you appreciate them, and how important the relationship is to you. When your partner feels valued, they will feel secure in the relationship.  Try leaving notes of appreciation in places you know your partner will see them. If you demonstrate appreciation with gifts, be careful your partner doesn't feel like you are trying to buy your way out of trouble. Help out around the house to show them you notice and appreciate how much they do. Be patient with your partner while he or she learns to trust you again. This is out of your hands, and trying to speed the process along may cause your partner to feel you are not respecting their feelings.  Instead of focusing on something you have no control over (time), focus on the things you can control, such as being reliable and consistent.  Show your partner you have made long-term changes; don't just do things for the short term and then fall back into old habits.

Summary:
Communicate clearly with your partner. Ask your partner what they need. Call and/or text regularly. Plan activities to spend time together, without focusing on the betrayal. Express gratitude for your partner. Accept that it will take time.