Infidelity can be one of the most destructive things in a marriage. You say that it happened a while ago. It sounds as if you are going through a process of grieving – maybe you are grieving the loss of trust in your marriage. The grief cycle includes phases of anger, denial, bargaining, depression and finally acceptance. Since you’ve decided to stay in the marriage, I’m assuming you still like something about your husband. If he sincerely regrets his mistake then try to separate his past bad behavior from his current character. If you keep allowing his past betrayal to consume your thoughts, this will sabotage your current relationship with him now and cause you emotional exhaustion.
Repairing a marriage after infidelity takes conscious effort. Have you told your husband that you are feeling torn apart, and having difficulty coping? Would you both consider seeking professional marriage counseling? A therapist can help guide you through the process of healing. Things may never go back to the way they were before the cheating, but since you’ve chosen to stay with him, you owe it to yourself to choose personal attitudes that will help, not hurt you.