However, alarm bells began to sound when Mrs Hewitt and her husband, David Gray, met Al Amin Dhalla.
Relatives began to suspect he was hiding something like a previous marriage, but the truth was far more serious.
They discovered the Canadian citizen, who worked in the City, had served at least one jail sentence, for assaulting a family member, and had used at least three aliases.
Dhalla's obsessive violent nature emerged after Alison, 37, finally was persuaded to leave him, leading to Dhalla launching an arson attack on the family's 500-year-old thatched cottage.
Mrs Hewitt and Mr Gray were put under police protection, and while Dhalla was on the run he dressed as a doctor to track down Dr Hewitt at the hospital where she worked.
He had earlier been arrested with a cache of weapons including two crossbows, but had been let out on bail.
The family has disclosed how the UK Border Agency failed to act on warnings about the convicted criminal which they delivered months before his campaign of harassment.
It is the latest allegation of serious failure at the Border Agency, the troubled body which is being reorganised yet again after last summer's relaxation of security checks at ports and airports.
Mrs Hewitt, a former probation officer and lecturer, said: "The Border Agency should hang its head in shame. We came to them with important information and asked them for help, but they did nothing.
"Dhalla is the kind of man who seeks revenge. We will be looking over our shoulders for the rest of our lives."
Mr Gray said: "Dhalla got into Britain very easily despite his past, when we told the Border Agency he was a threat they did nothing and, on conviction, there is no guarantee that dangerous criminals will be deported."
Dr Hewitt met Dhalla in 2010 through an upmarket online dating agency, the Executive Club of St James.
Alison's mother - then a widow - and stepfather, met Dhalla when Alison brought him to their wedding in June that year.
They were both perturbed by his reticence about his past. During a trip to the family's Spanish villa, a glance at Dhalla's passport revealed the woman he called his "aunt" was his mother, and that he had lied about his age and how long he had lived in Britain.
Mrs Hewitt, 66, and Mr Gray, 65, an engineer for the missile systems manufacturer MBDA, feared he was hiding other secrets.
Dhalla reacted with rage when he realised they had looked at his passport.
A few days later he sent a letter to Mr Gray's employer alleging he was a spy, selling secrets to foreign powers and terrorists.
Without their daughter's knowledge, Mrs Hewitt and Mr Gray hired a private investigator who found Dhalla had a conviction for assaulting his uncle with a weapon, that he had used three aliases and had a 10-year ban from owning firearms in Canada.
"We feared for Alison's safety," said Mr Gray. "We were amazed that he had been able to get into Britain so easily. He had lied about his past and we decided to tell the authorities what we'd found out."
They emailed the Border Agency in November 2010, while Dhalla and Dr Hewitt were in Canada on holiday, and said Dhalla had obtained a British visa under false pretences and detailed his travel plan.
But Dhalla came through Heathrow without being asked a single question.
Letters to the UKBA and Theresa May, the Home Secretary, were unanswered.
Mrs Hewitt said: "For the Border Agency not to follow up was gross negligence. We wrote to Theresa May months before the arson attack. She should have seen he was dangerous and done something about it."
When Dr Hewitt finished with Dhalla he was evicted from her flat in Brighton, prompting malicious letters to her mother's neighbours in Aston Abbotts, Bucks.
When Mrs Hewitt and Mr Gray went on holiday to Lundy Island in the Bristol Channel in April, the Canadian was arrested in a field in Wiltshire target-shooting with weapons including two crossbows and an air pistol.
In his van were masking tape and tools. The address of the couple's holiday cottage was logged in his sat nav.
He was released on bail and two days later set fire to Mrs Hewitt and Mr Gray's thatched cottage, which neighbours extinguished.
The next day, Dhalla tried to burn down the police station, and the couple were airlifted off Lundy and kept under police protection while he was on the run.
Dhalla, 42, was convicted of nine charges including two counts of harassment, arson, attempted arson, possessing an offensive weapon and perverting the course of justice.
He is due to be sentenced next month.
Mr Gray said: "Our primary concern is for our safety … I would like reassurance that he's never going to set foot in this country again. All the UKBA will say is that he will be 'considered for deportation'."
After Dhalla's conviction at Lewes Crown Court last month, the Hewitts were told another person may be intending to cause them harm, and were advised to enter a witness protection programme. Mrs Hewitt said: "I've lived in this house for 27 years. Why should I cut myself off from my friends? I'm not a criminal."
A Sussex police spokesman said: "We contacted the family about a potential threat, which is under investigation. The family is being appropriately supported."
A Home Office spokesman said: "This was a terrible case and this individual is now in jail where he belongs.
"We believe all foreign criminals should be removed from the UK and we will seek to deport Mr Dhalla at the earliest opportunity."