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My sister is a compulsive liar – should I cut her out of my life? The Guaridan.

Dear Annalisa

My middle (younger) sister is a compulsive liar and it’s got to the point where I feel I must cut her out of my life. She suffers from mental-health problems and the lying has got increasingly worse over the past two years, since she met her first boyfriend. They got engaged in under a year but in the time she has been with him her behaviour has got worse. They constantly argue, there have been suicide attempts and she is unable to spend time away from him, although from the outside it appears that they make each other miserable.

They have destroyed our family life to a point where we rarely all spend time together – we used to be close. They make constant calls to my parents each time they fall out and if they are not falling out with each other they make terrible accusations about me or my younger sister to try to cause family rifts.

I have repeatedly cut contact with them only to feel guilty and let them back in just for her to attack me at the first opportunity, saying I have an eating disorder and am an alcoholic. The truth is that outside my family I have a great life: I have a very successful career, a large group of friends and a supportive partner. Everything is going well and I am sick of constantly being dragged down by my sister and her fiance.

My parents refuse to reprimand her for her behaviour as they are terrified that anything negative they say will cause a suicide attempt. She holds our family to ransom: any family time has to be arranged around her or my parents suffer weeks of her terrorising them.

I feel this kind of behaviour can’t be tolerated for ever as it’s putting my parents under huge amounts of stress, but there is no way of getting through to my sister; as far as she’s concerned, her behaviour is always someone else’s fault. Although I appreciate how hard it is to live with depression and mental illness, I don’t believe that this fully excuses her actions.

How can I help my parents? Or is the solution to cut her out of my life and focus on my own happiness?

Does everyone in your family feel the same? I hear that your parents feel powerless to act but do they feel the same as you do? Does your sister? If they do, then it’s a shame that you can’t all come together to tackle this behaviour. Is your sister under any sort of medical attention?

I consulted Dr Angela Mooney, a counselling psychologist who specialises in compulsive behaviour addiction (bacp.co.uk). She explains that if “someone acts out a compulsive behaviour such as lying, it can originate from a fear of being criticised”. Put simply, people lie when they fear the reaction the truth will bring. Mooney feels that this behaviour had probably started in childhood: “The compulsive need to lie is a defence, a learned defence: you tell a lie rather than face the consequences of the truth, or the reality of life.”

You don’t mention the early years in your family and what childhood was like. Mooney noticed that you seem to take a parental role in your family (not unusual for the eldest) and that there seemed to be a lack of boundaries. Perhaps because that’s how it was as you grew up; perhaps your parents over-involved you in things they should have dealt with.

The key for you is boundaries. You need to set some up, especially in relation to what goes on between your sister and your parents – you need to try not to get involved. This won’t be easy but it may be your saving grace, a safe strip of land between what happens now and total disengagement – which never works out quite the way people plan.

“An emotional separation needs to happen,” says Mooney. “There’s a lot of emotional reaction and enmeshment in the family. Your sister draws you into her drama and you react – that may be how your family has experienced caring.

You can’t change anybody else but you can change your own reaction because that’s the only part of the equation any of us has control over. So you need to change these familial patterns. If necessary, Mooney suggests talking to your sister and saying that you will no longer be drawn into her dramas – “I care but I can’t get involved any more” – and then be consistent.

Don’t react. If your sister spreads rumours about you within the family and you hear about them, just say simply, “That’s not true” and move on.

This will be hard to begin with – you are used to doing things in a certain way. If necessary, make your own arrangements at Christmas or say, “Let me know when plans are finalised.”

“If you carry on like this,” says Mooney, “you’re not going to save your sister. Your part in this is to keep the same consistent rules and thus change the family dynamic. You may not feel great [about it] at first, but you will feel better.”

This article first appeared in The Guardian Family section on 16 October 2015.