The 52-year-old is best known for her appearances on Embarrassing Bodies and This Morning.
Dawn and Graham – who have three grown up children together – are said to have split amicably and Dawn has moved out of the family home.
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The star's TV appearances may have been a contributing factor in the split, according to the Sun.
A source told the publication: "They have drifted apart. There's a feeling being a star has gone to her head."
However, a friend of Dawn's told Express.co.uk that the allegation couldn't be further from the truth, and the fact that she still works as a GP in her local practice shows she has not changed since becoming well-known.
Dawn and Graham had been living together in rural Gloucestershire, where they are both GPs at local surgeries.
An expert in women's health, Dawn has starred on Embarrassing Bodies since 2007 and also gives medical advice on Woman's Hour on BBC Radio 4.
She often appears on This Morning as a medical expert.
The star featured on the ITV show yesterday when she reviewed the latest health headlines with Phillip Schofield and Holly Willoughby.
She also recently explained how a bionic penis – the Titan Touch – can change lives.
A spokesman for Dawn said: "Dawn and her husband separated in June 2014.
"It is always sad when a marriage ends but the split was amicable."