Step1
Awareness:
Infidelity is not just the issue of having sex with another person outside your marriage. Infidelity involves a break in trust, disloyalty, dishonesty, secrets and the possible exposure of both of you to sexually transmitted diseases (STDs). (If you know for a fact that your spouse has had sexual relations with another person you should be checked by your physician and have a blood test to be certain.)
Step2
Counselling:
I would recommend that the first thing you do is talk to your clergy or a marriage counsellor about the situation. They can help you follow a course of action and decide what is the best approach in talking to your spouse, what options you may have, and possible consequences. Counselling may help you and your spouse resolve the real root issues that led to the infidelity. They will also help you and your spouse work on strategies to save your relationship and marriage.
Step3
Confrontation:
(Most married men do not leave their wife for a lover. If they leave it will be for incapability, financial reasons, unhappiness or other reasons. Seldom is it for sex.)
First, you must ask yourself what you want? Do you want to stay in the relationship? Do you have real evidence of infidelity or are you going on innuendos? Either way you need to meet with him, one on one, and discuss the issue. You should be honest, tell him what you think or know and tell him how this makes you feel. Also tell him what you want out of the relationship, and what your expectations in the future are.
If he is honest with you, then you should both go see a professional counsellor, who will help you learn to be a couple again, build trust and save your marriage.
Step4
Outcomes:
There is no guarantee that confronting your spouse about infidelity will stop his being unfaithful. However, marriage is about love, communication, friendship and trust. All of us go through periods in our life where we feel less than adequate, unloved, insecure, or do stupid mistakes in life. Confrontation is the only way to discuss this with your spouse and make an attempt to resolve the situation and save your relationship.
You also run the risk of your spouse leaving. However, relationships grow on mutual experiences, honesty, openness, love and friendship. Secrets, dishonesty and infidelity will not go away unless they are addressed. Your spouse should be treated as your best friend, and you would tell a friend if you thought they had betrayed you.