Should You Trust a Partner Who Cheated Before?

Rekindling a romance is easier than rebuilding trust. Savvy Psychologist takes an evidence-based look at what relationship science has to say about finding love after infidelity.

Jade Wu, PhD
6-minute read
Episode #344
The Quick And Dirty

If you're ever wondering whether you should rekindle a relationship with someone who has betrayed you in the past, be very deliberate in your choice. Instead of letting yourself be swept back into a relationship, take stock of this ex-lover's past behaviors and personality tendencies. Know that infidelity tends to be at least partially about the person's own baggage, not just because of a chance encounter. Consider all the reasons why you may or may not want to be in a relationship with them agian, because the real question is not whethr they'll cheat again. The real question is whether you want to give your time and love to them, based on everything they have to offer, past and future.

If you’ve ever had a messy breakup, you know that it’s never just over and done. There are dramatic fights, sweet reconciliations, doubt, betrayal, heartbreak … all the best of 90’s rom coms. But what happens when the movie has a sequel? How do you decide if you can give a relationship another try? What if there is a history of trust issues?

A Savvy Psychologist listener named Amy reached out recently to ask about a ghost from a relationship past. She wrote:

“I had a fiancé about 20 years ago who left me for another woman. We never really lost touch and now have rekindled. We have some great chemistry but I’ve always heard, ‘Once a cheater, always a cheater.’ I’m afraid the past will keep haunting me and holding me back from giving my all and completely trusting him again.”

Amy, I want you to know, first and foremost, that anyone in your situation would be having a hard time with this dilemma. There are many feelings here -- fear, hope, doubt, perhaps a touch of resentment. And many of us can relate to the uncertainty of balancing these feelings when love and betrayal are involved.

As usual, the answer is complicated. And today, I’m not going to sugar-coat anything. We’re going to be brutally evidence-based in considering this dilemma.

First, let’s boil down the question to three things we need to consider:

  • How true is the age old adage, “Once a cheater, always a cheater”? What predicts whether a person will cheat again?
  • How does past infidelity affect the quality of your relationship going forward?
  • What else should we consider when trying to decide to rekindle a past relationship?

Now, let’s look at what psychological research has to say about these topics:

1. Infidelity is a mixed bag

In the movies, people fall into affairs by accident. A chance encounter. An irresistible glance. A touch of the fingertips. A whirlwind romance ensues -- one that nobody saw coming. If it’s the type of story with a happy ending, they either follow their heart and end up happily ever after with the new partner, or they feel terrible about their one-time mistake and it ends up strengthening their marriage.

In real life, infidelity is more predictable. About 2-4% of married people have had extramarital sex in the past 12 months. Who’s more likely to have done it is not totally random. There are actually some consistent predictors.

For example, people with higher narcissism personality traitsinsecure attachment styles, and more open attitudes towards casual sex are more likely to have cheated. People also have “sexual personalities,” referring to how easily they become sexually excited, and how inhibited they are when making love, and these traits can be associated with higher likelihood of engaging in infidelity

More importantly for our dilemma, people who have previously engaged in infidelity were also more likely to do it again.

Of course, this is not to say that someone who has cheated will definitely do it again, nor that they are narcissistic or have insecure attachment. We’re talking about higher likelihoods when we take a bird’s eye view of a large group of people and their patterns. And of course, we can’t discount the obvious: People in unhappy relationships with incompatible partners are also more likely to cheat.

When we look at the overall picture -- some portion of why people cheat is predictable, some seems up to chance, some we don’t understand. But an important thing to note here is that
infidelity is (at least partially) founded on personality traits and personal history. Not just on a chance encounter, on a one-off mistake.

People with higher narcissism personality traits, insecure attachment styles, and more open attitudes towards casual sex are more likely to have cheated.

2. Infidelity may taint the a relationship

Again, having cheated before isn’t a guarantee of it happening again. People change their behaviors, their way of relating to the world. Relationships change. Circumstances do, too.

But another thing to consider is that even when infidelity doesn’t happen again, the past can affect how we feel about the present. This is not even something we might think about on purpose. We might, at a basic perceptual level, see our partners differently because of the past.

For example, research has shown that people who have cheated or been cheated on tend to be more sensitive to possible cheating behaviors. They’re more likely to see ambiguous actions like having a meal with someone as cheating, compared to people who have never been involved in infidelity.

Perhaps this is why a study on marriage counseling has shown that, when a couple has infidelity in their past, it’s hard for marriage satisfaction to be totally back to normal. Even with an intervention that improves the relationship, it never quite improves to the level that it would be if there was no infidelity in the past. 

3. Make sure it's your decision

So far, the evidence seems rather pessimistic. But of course, we’ve only focused on the issue of infidelity. A relationship is about a lot more than not cheating! For Amy, of course this is forefront in her mind as she deals with the dilemma of whether to rekindle a relationship with a previous partner, from decades ago, who had left her for someone else. But I bet this is not the only thing that matters to her in the relationship.

I imagine that for any relationship, whether old or new, we care about our compatibility with the other person, how they treat our family and friends, whether they’re a dog or cat person, and so much more. So let’s not forget the other things that matter. If you're reconsidering a relationship, ask yourself:

  • Why do you want to be with this person?
  • What do you like about them?
  • What do you look forward to in your future with them?
  • What things do you have in common? And how do you cope with the things you don’t have in common?
  • How do they make you feel about yourself?

If you can easily and sincerely answer these questions in a way that points to a loving and fulfilling relationship, it’s a good sign. But if these feel shaky … well, that’s good information, too. If the fact that they left you before, cheated before, treated you unfairly, lied to you, or ended up doing these things to other of their partners makes you feel uneasy … listen to your gut.

4. Be deliberate 

Don’t be swept along. We know from relationship research that when someone decides to be in one, they’re more likely to be happy in their relationship than if they “slid” into one.

You know how sliding into a relationship works -- you say “why not” to a date, and you have enough of a good time that you go on a second, and a third, and you meet their parents because they happened to be in town, and before you know it, they’ve moved in (because rent is so expensive, right?). You didn’t have a good reason to break up at any point along the way.

But importantly, you didn’t really make the decision to be in this relationship at any point, either. You were just sliding into something that defines a major part of how you spend your time, your emotions, your self.

And if you are in a situation like Amy’s, where you’re grappling with the question of whether you can trust someone again after they had betrayed you, it’s more important than ever to decide instead of slide.

While you do it, don’t be distracted by the idea “Once a cheater, always a cheater,” because ultimately we just don’t know for sure. And more importantly, that’s not the real question. No matter what they or other people say, the question is not whether you can forgive their past mistakes. The real question is: Do you respect and love this person, do they respect and love you, and do you want to give your time and your heart to this person?

Amy, thank you for your question, and I wish you all the best in life and love.

If the fact that they cheated before, treated you unfairly, lied to you, or ended up doing these things to other of their partners makes you feel uneasy … listen to your gut.

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All content here is for informational purposes only. This content does not replace the professional judgment of your own mental health provider. Please consult a licensed mental health professional for all individual questions and issues.

About the Author

Jade Wu, PhD Savvy Psychologist

Dr. Jade Wu was the host of the Savvy Psychologist podcast between 2019 and 2021. She is a licensed clinical psychologist. She received her Ph.D. from Boston University and completed a clinical residency and fellowship at Duke University School of Medicine.