When I was 21, I went on a girls’ trip with university friends. Over dinner, one of the girls, who was known for being a liar, announced she had just heard from her doctor that she had cancer and needed chemotherapy. She never had chemotherapy and most of the group (especially me) stopped socialising with her after that. Five years later, she admitted she had been lying. Recently, a new person joined my work and I think she may be a liar of similar proportions. We get along very well, are a similar age and are both chatty. She is also an over-sharer. According to her, this has been the worst six months of her life, involving injuries, escapades and traumatic events, some of which feel untrue. I feel I have to believe her or I’ll be the worst person ever. Yet, my instincts and life experience tell me these things are probably fiction or at least heavily exaggerated. Recently, she told me some blood tests are showing she has a cancer. What do I do if she confirms she has it? I have huge empathy for her and give her a lot of time because she is sweet. But I’ve started telling my non-work friends her stories and being a bitch behind her back. No one likes to be lied to. But I went to psychologist and psychoanalyst Prof Alessandra Lemma, who felt the “central issue here is not really whether your new friend is actually lying – although of course that matters on one level – but the way you’ve been placed in a painfully familiar emotional position”. Lemma felt this is informing your reactions. “You’re not encountering your friend in a neutral way, but through the afterlife of a previous relationship in which illness, manipulation, guilt and mistrust became tightly tangled together.” I found myself wondering if you grew up with people who exaggerated/lied and if you were constantly searching for the stability of truth. This is an exhausting existence for a child. Of course, it may have nothing to do with that, but these “tall tales” do seem to land heavily with you. Lemma also pointed out that you seem caught between two rigid positions: “Believe these dramatic disclosures or risk becoming a cruel, unfeeling person. That you say you’d be the ‘worst person ever’ is a revealing statement. “Uncertainty seems hard for you to bear,” continued Lemma. “It seems you feel compelled to make a moral judgment before you can settle internally. But in fact you don’t need to decide in any definitive way.” Lemma points out: “You have a split in your attitude to your friend: on the one hand, you describe her as sweet; on the other, you are starting to gossip about her, which itself becomes a kind of lie as you are not truthful with her about what you feel.” We both felt you didn’t need to become a detective. “You can respond with ordinary human sympathy – ‘That sounds hard’, ‘I’m sorry you are going through this’ – without taking on the burden of deciding whether every detail is true,” Lemma said. You will always encounter people who lie or exaggerate. The key is to have boundaries. “The task for you is to tolerate some uncertainty, to be neither credulous nor punitive,” said Lemma. “You may find it useful to ask yourself not only, ‘Is this person lying?’, but ‘Why do I feel so compelled to decide?’ The truth lies in the suffering that the lie points to.” Every week, Annalisa Barbieri addresses a personal problem sent in by a reader. If you would like advice from Annalisa, please send your problem to ask.annalisa@theguardian.com. Annalisa regrets she cannot enter into personal correspondence. Submissions are subject to our terms and conditions. The latest series of Annalisa’s podcast is available here.