Okay, I have to say it, even though I know it won’t do any good. Don’t let yourself go there! But you will. It’s inevitable. You want to try to figure out what went wrong, so you can hopefully stop it from happening again. Trust me–even if you knew there were things you did wrong, and you fixed every one of them, there’s no guarantee it wouldn’t happen again. (Sorry!) 
First, please understand that I’m not saying it’s your fault that someone cheated on you! And I’m not saying that he was justified in doing it, either! What I am saying is that people tend to try to justify their actions by pointing out their partners’ flaws or negative traits. For example, how many times have you heard men say, “She just let herself go,” or “She’s gained so much weight,” or women say, “All he cares about is the TV,” or “He never listens to me”? 

Even if you were perfect in every way, a serial cheater would say, “She’s just too perfect; she makes me feel inadequate.” There are some people, whom I call ‘serial cheaters,’ who would cheat, no matter whom they were with or what the circumstances. If you’re with a serial cheater, don’t worry about how you could improve yourself or the relationship! Just get rid of him!!
However, if your partner is a good, decent person that you believe is actually regretful about the indiscretion, and if you believe you could forgive and trust this person again, you might want to give it another go. But I strongly urge you to get couples counseling before you recommit to the relationship. DO NOT think that counseling is a magic pill, though. Some couples can work through instances of infidelity, and some can’t. It takes a very strong, secure person to be able to give a cheater another chance. If you choose to do that, I also vehemently urge you to make sure that God is a part of your marriage or relationship. Relationships are hard enough without thinking you don’t have God helping you.
Whether you decide to continue the relationship or not, it’s always good to take a long look at it. Obviously, he cheated on you, which always involves deception, if not blatant lies. But what else was wrong in the relationship? Make a pros vs. cons list of your partner, and make one of the relationship. Ask yourself the following questions:

  • Do I love him?
  • Does he love me?
  • Was I happy with him before he cheated?
  • Was he happy with me before he cheated?
  • Have we been emotionally, as well as physically, intimate in recent months?
  • How often do we make love?
  • Is the sex loving and thoughtful, or is it hurried and selfish?
  • Does he care about my feelings?
  • Do I care about his feelings?
  • How well do we get along?
  • Do we want the same things in life (have the same goals)?
  • Have we grown apart?
  • Is he committed to the relationship?
  • Am I committed to the relationship?
  • Why are we together (good sex, children, money)?
  • Do we respect each other?
  • Do we like each other?
  • Do we enjoy being together (have fun together)?
  • Do we allow each other freedom to be ourselves?
  • When we disagree, are we civil, or are we abusive?
  • Do we get violent?
  • How did we get to this point?
  • What is his part in getting here?
  • What is my part in getting here?
  • Why do I want to stay with him?
  • Do I want him because someone else does and I can’t stand to lose, or do I want him because I love him?

After examining the relationship, it’s time to take a good long look at yourself. Even the best of us contribute in some ways when we are in a relationship that is crippled and/or dying. We feel hurt, so we lash out. Or maybe we take the passive-aggressive route and “forget” to pick up his dry cleaning, or “forget” to move the wet towel off her side of the bed.
Most of the time, men who cheat on their partners say that it’s because of the way the new (“other”) woman makes him feel. That’s not just about chemistry. It’s also about the way she makes him feel about himself, too. We might not be able to change the chemistry we have with someone, but there are other aspects of the relationship over which we do have some control.
As previously mentioned, cheaters like to try to justify their actions by pointing out the shortcomings of their partners. Sometimes those are just words–lame excuses for what they don’t want to take responsibility for. But sometimes, there is validity in those words. Again, I’m not blaming the victim or condoning infidelity! I’m just saying that it is what it is. 
Here’s an example:  Let’s say that a woman tries repeatedly to talk with her husband about issues that are important to her. Either he’s “too busy,” or he belittles and denigrates her. She has a male co-worker, however, who is a good friend, and he listens intently to her problems. Because the co-worker is meeting a need that her husband refuses to meet, she becomes vulnerable and develops romantic feelings for him. It’s not right, and it’s not okay, but it’s understandable. 

This is another example:  A man wants to have sex with his wife. She ‘allows it’ maybe once or twice a month, but only with lots of restrictions. No oral (giving or receiving), no kissing, no ‘talking dirty,’ no touching of “undesignated areas,” etc. He feels undesirable and inadequate, as well as unloved. He meets a woman on a business trip who is attractive, and she seems to be interested in him. They talk, share a dinner and drinks, and then she touches his leg. Sparks fly! She begins to fill the void in him that his wife has no interest in filling. They kiss, and he’s toast! Again, not okay, and certainly not right, but it’s not difficult to see how and why he would be vulnerable.
We all have needs, and some of them are basic, like love and security. Some of us have stronger sex drives, while others have a much deeper need for emotional intimacy.
When we enter into a marriage, we are making a commitment to at least attempt to meet the needs of our partners. If those needs are not met, they become vulnerable to temptation.
Humans are weak, especially with regard to sex, which makes it  difficult to resist. When we have a loving, affectionate, considerate partner who meets our needs, we are much stronger when faced with temptation. Maybe it’s because we can’t justify cheating on someone like that. If, however, we feel neglected and unappreciated, we are much more likely to stray.
The moral of this story is that though there is no magic pill (or silver bullet), being an affectionate, attentive, and considerate lover, partner, and friend is the best defense against infidelity. Still, unfortunately, there are no guarantees.