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When Nathalie ­Kelderman signed up to an online dating site she was looking for love, romance and even marriage.

And with as many as one in five lasting relationships now beginning online, she thought there was little to be worried about.

But Nathalie was to learn the hard way that what can look like a match made in heaven on screen, can just as quickly turn into a horrific nightmare.

In March this year, Sebastiano Mauro, 43, who she had dated for just five months, was jailed for five years after slashing Nathalie’s prized horse Jessie and plotting to inflict grievous bodily harm on her too.

“Dating sites are great at telling you how they can help you find a lasting relationship or even marriage – but they don’t highlight the dangers,” says Nathalie, 37, from St ­Albans, Herts.

“I was sucked into an abusive relationship because of internet dating.”

In October 2010, water company shift manager Nathalie signed up to Match.com after her eight-year relationship floundered and she found herself struggling to meet new people.

“Once you reach a certain age, it just gets harder to date,” says Nathalie.

“I thought online dating was the answer – you’re ­instantly connected with other singles.”

While her first forays into finding a ­potential suitor led nowhere, in December 2010 Nathalie was messaged through her Match account by Sebastiano Mauro, a ­dark-haired Italian who quickly charmed her with his sense of humour.

“I’d put on my profile that I preferred men with short hair,” she says. “Seb had long, black locks and the first time he got in touch he joked, ‘how short is short?’

“He made me laugh, and it showed that he’d actually paid attention to my profile.”

Days later, in January last year, the pair met for lunch halfway between Nathalie’s home and ­surgical nurse Mauro’s pad in Chatteris, Cambridgeshire.

“There was an ­instant connection between us,” says Nathalie. “Seb was immaculately dressed in a ­top-brand suit.

“He was ­quietly-spoken and perhaps a little eccentric, and had those classic Italian looks.

"We talked for hours and found ourselves swapping ­intimate life ­stories.

"He was Sicilian-born, and had come to the UK 10 years earlier and married a Scottish woman.

"They’d had a son and daughter ­together, but Seb said it had been an unhappy marriage, lacking in love and affection.”

Things happened very quickly from there.

“A few days after we’d met, he came to mine to stay the night – but ended up staying for two.

“We were soon seeing each other every week. I was completely swept off my feet,” she recalls.

Flush with cash after a stint working on a cruise liner as the ship’s second medical officer, Mauro showered Nathalie with gifts and lavish meals.

But alarm bells began to ring when, just months after they’d started dating, Mauro developed a ­possessive streak, ­imposing bizarre restrictions on her.

“I’m a keen horse rider and he resented the time I spent at the stables,” she says. “He started saying I could have half an hour riding before I had to be home.

“I’d find myself rushing back from work or drinks with friends because I knew if I was late there’d be an argument.

“Our relationship veered from loving to complete chaos, then back again. Before long, I couldn’t even think straight.

“I should have walked away, but I’d come out of a passionless relationship and Seb seemed head over heels in love with me.”

By May last year, barely five months in, Nathalie was having serious doubts about the relationship.

But each time she tried to end it, Mauro won her over with apologies and promises of undying affection.

However, an altercation in July last year after Nathalie nodded hello in the park to a passing jogger finally made her end their tempestuous ­relationship.

She claims: “I knew the jogger but Seb went ballistic, screaming I would make ‘an ­excellent whore’ and he threw me to the floor and kicked me. It was frightening.”

Mauro was charged with assault and bailed on condition that he stayed away from Nathalie. But he flouted the ban, bombarding her with phone calls and texts.

“Over the next week, he wouldn’t leave me alone – it was terrifying,” she says.

“He left ‘I love you’ notes on my ­windscreen, tried to get in my apartment block by ­pretending to be a cleaner and constantly called and texted me.”

But Nathalie refused to rekindle their romance. Then, on the morning of July 11, Nathalie got a call from the stable manager where she kept her horse just as she was preparing to go for her ­morning ride.

“He said Jessie’s leg had been cut to the bone and that the wound didn’t look like an accident,” she says. “He knew the problems I’d been having with Seb and said he’d seen him hanging around the lane nearby.

“I called Seb straight away and told him what had happened, but he acted as though he was appalled I could think that of him.

“When I saw Jessie’s injury I was ­absolutely mortified. Thankfully, a vet was able to stitch up the wound and Jessie was OK.”

(Image: A M Sorenson)

On examining CCTV cameras it was clear Mauro had been hanging around the stables and the police arrested him the same day.

He was remanded in custody for two months before being bailed, and was warned to stay away from Nathalie again.

“I was terrified. I spent two days printing flyers with Seb’s photo on, warning my neighbours and work colleagues to call the police if they saw him,” says Nathalie.

Just three days after his release, Mauro drove from Chatteris to St Albans and parked opposite Nathalie’s flat.

Luckily, police officers doing spot checks on her discovered him lurking outside the apartment. He was armed with a chilling torture kit of knives, screwdrivers, scalpel blades, a ­tourniquet, latex gloves and syringes filled with his own blood.

“When the police came and told me what they’d found I felt numb,” says Nathalie.

“It was absolutely bloodcurdling. Who knows what might have happened if they hadn’t spotted him?”

Once again Mauro was remanded in ­custody. Fearing that he might have made contact with other women, Nathalie checked his Match account only to find he had ­reactivated his profile when he’d been ­released from custody in September.

“There was a link on Seb’s profile to ‘report a concern’ and I emailed Match through that, telling them what had happened, going right back to his first arrest in July 2011 for ­allegedly assaulting me,” she says.

“I even included contact information for the police officers dealing with my case. But I heard nothing from Match – no email, no apology, not even a courtesy call.”

Nathalie followed up her email by phoning Match in December 2011 and was assured by a customer services representative that the matter would be investigated.

But incredibly, Mauro was still listed as a potential date on the site a month after his trial in March this year.

Mauro was found guilty at St Albans crown court and jailed for five years for injuring Jessie and going equipped for burglary ­intending to inflict grievous bodily harm – he was cleared of assault.

“I spent three gruelling days on the witness stand giving evidence from behind a screen,” says Nathalie. “Emotionally, ­psychologically, I just couldn’t handle seeing him.”

Match only removed his profile in May after being contacted by a reporter.

“I’m flabbergasted that Match took ­everything I’d been through so lightly,” says Nathalie.

“I could have been chopped up in my flat and his profile would still be there.

"What would it have taken before they sat up and took notice? I shudder to think.

“Men like Seb can use these sites to pick and choose from a list of potential future victims – it’s high time dating agencies met their responsibilities head on.”

A spokesman for Match admitted mistakes had been made but said policy had been changed and staff retrained.

He added: “The safety of our members is important to us, and in light of his conviction, we can confirm Mr Mauro’s profile has been removed.”

Nine months on from his conviction and Nathalie is still living with the emotional fallout.

“How could something potentially so beautiful turn out to be so ugly and dark?” she asks.

“I’m very wary about web dating now. I’ve met someone else online but I’m not the person I used to be and he’d be the first to agree that I have huge trust issues.

“I’ve spent time researching online about what I went through, and it all seems so clear – Seb’s ­impulsiveness, mood swings and instances of throwing money around were all signs of the type of ­personality that can lead you into a dangerous relationship.”

Nathalie hopes others will learn from her experience and urges everyone to follow her three golden rules of internet dating: “Don’t believe everything in a profile, know the warning signs – and trust your gut.”

By Robin Eveleigh.