Articles by Jacqueline McDiarmid, Break ups, Couple's counselling, Family counselling, Mental Health, Narcissist, Post Separation, Relationships

Why did my partner cheat on me?

At the Sydney Couple and Family Specialists we see many couples for marriage and relationship counselling – and probably one of the most common (and painful) presentations is when one person has betrayed the other.  There are lots of different ways to commit a betrayal – kissing someone else, sex with someone else, an emotional affair (without sex), or a full blown affair discovered. 


The injured person always asks a Couples Counsellor like me – “Why did he/she do it”? Sometimes over and over again. In order to forgive a relationship betrayal – if they want to stay in the relationship – the injured partner has to be able to make sense of it. If the injured person wants to leave the relationship, they need to be sure it won’t happen again in the next relationship.

Over my 20-plus years of working with couples I have observed a lot of betrayal – and heard from both ‘sides’ of the relationship. Of course every situation is unique, but there are patterns and commonalities.

Here are 10 common reasons why people cheat on their partners:


  1. Underlying and often untreated mental health – typically depression (in my experience). Often people with depression blame their primary relationship on the way they feel and seek to “medicate” with the excitement of somebody outside of the relationship.  It is a way to avoid the depression and the feelings that come with it.  Please note that most people with depression do not betray their partners – but a lot do.
  2. Alcohol and drugs – I come across many people who have binge drinking problems which lead to kissing or having sex outside the relationship – behaviour that would not happen if they were sober. The underlying problem here is potentially alcohol and/or drug addiction.  Usually these betrayers are extremely remorseful and understand the hurt they have caused.  They obviously need to actively work on their problems with alcohol and drugs in order to stay faithful to their partners.
  3. Loneliness – lack of connection, and the feeling of being lonely in their relationship can lead to a person having an affair or committing a betrayal. This is even more likely to happen if the person believes they can’t exit their primary relationship due to children or financial reasons.
  4. Affairs can be a way to exit out of a relationship. Some people find it too emotionally painful to leave their partner, even if constant conflict or lack of connection suggests that separation might be a good idea.  They seek out a  connection with someone else to help them to find the courage to leave.
  5. Family stress – I see a lot of affairs in families where there is a diagnosis of AD/HD or ASD in a child. Parenting a child with extra challenges can bring stress and unhappiness to a relationship, and to family life in general. Sometimes a parent will seek an affair to ease or manage this stress.
  6. Sexual addiction. Just like alcohol and drugs, some people struggle with sexual addiction and commit multiple betrayals. This is behaviour they have often been showing since their teenage years.
  7. Narcissistic Personality Disorder. A LOT of people going through a separation tell me their partner is Narcissistic, but true Narcissists are rare. If you are unfortunate enough to be partnered with a Narcissist and they commit a betrayal, they will have no empathy for you, show no remorse, and will expect you to just get over it. In fact, a Narcissistic person will be angry with you if you continue to be distressed about the betrayal.
  8. Lack of sexual fulfilment in the primary relationship. I don’t need to elaborate.
  9. There is a family history of betrayal. If that’s the case, the affected partner may not have learned how to communicate his/her feelings and thoughts healthily. Poor communicators often get into a pattern of affairs and betrayals. A lack of attachment or security in childhood can lead to adults acting out – and having affairs.
  10. Revenge. Unfortunately, this does happen. One partner will have an affair to hurt the other to ‘pay them back’ for something.  If it’s about revenge, the person having the affair wants their partner to find out.


Whether you are the betrayer, or the betrayed partner in a relationship affected by affairs, you should seek couples counselling right away.


The longer you leave it, the more your relationship will suffer – and it may not recover. Individual relationship counselling is also a good idea for the injured so they can work through their thoughts and feelings about what has happened to them in private.  A relationship counsellor can support you to make the right decisions about your current and future relationships.

About Jacqueline

Jacqueline has been in private practice for more than two decades, helping individuals, couples and families. She has extensive experience in couple and family therapy and is considered a specialist in these areas.

In her clinical practice, she has helped people deal with complex trauma, affairs, complex mental health issues, eating disorders, adolescent behavioural problems (including self-harm and suicidal ideation), behavioural issues in young children which are impacting parents and families, relationship issues and post-separation work.

Jacqueline works with many different dynamics: couples, parents, families with young children, same-sex couples, foster/adopted families, families with teenagers and also adult families. She is particularly interested in helping parents of children with behavioural issues, or with diagnosed conditions such as anxiety, ADHD, ASD and so on.

Although Jacqueline’s work is supportive and friendly, she will challenge her couples and families to make the necessary behavioural changes, to repair relationships and to move towards healthier communication styles in the future.

Jacqueline’s style is direct and fast paced and she is known for quickly getting to the heart of the matter. Clients report that they feel safe and understood with Jacqueline.

Qualifications and Professional Membership

Jacqueline has a Masters in Couple and Family Therapy (UNSW). She has a Bachelor degree in Counselling and Human Change, and a Diploma in Psychotherapy and Counselling.

Jacqueline is a Clinical Supervisor for Counsellors and Therapists. She lectures in couple and family therapy at Masters and Post Graduate level, and is currently Head Lecturer for the Couple and Family Therapy course (Masters) at the Jansen Newman Institute. She has been a Lecturer at the University of Western Sydney and Sydney University, and continues to guest lecture at other tertiary institutions.

Jacqueline is also the Director of the Couple and Family Training Centre where she runs regular professional development workshops and seminars for Therapists, Counsellors, Psychologists, Social Workers and Health Industry Workers who are looking to gain skills in this specialist area.

She is a Clinical Member of the Family Therapy Association of Australia and a Clinical Member of PACFA.

If you feel as though you could benefit from talking with a Therapist please contact  The Sydney Couple and Family Specialists on 02 8968 9397 or email

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