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Greg, a Canadian lawyer, is 28 but he's already had 11 serious relationships. He says each of those relationships ended with infidelity, on his part, and severe self-doubt on the part of the women. He is a self-confessed "gaslighter".

"Looking back it's clear that I was gaslighting the women and slowly making them second-guess their version of reality," he says.

He's speaking out now to give insight into the mind of a gaslighter, and to warn women of the tell-tale signs.

Gaslighting has been described as psychological abuse where false information is deliberately presented to the victim - the purpose being to make the victim question their own memory and perception of events.

Greg learned that he was a gaslighter recently, while in therapy.

He pinpoints the start of his behaviour to a relationship when he was a 21-year-old law undergraduate.

Paula was four years older and completing a master's degree. Greg describes the relationship as "romantic but unsteady". He soon began sexual encounters with other women behind her back.

But Paula was an intelligent woman and soon picked up that Greg was being unfaithful to her. Greg says that in order to continue cheating, while still maintaining their relationship, he had to "alter her reality".

He began identifying "techniques and pathways" in which he could manipulate Paula - laying the groundwork in order to make the lies that would come later more believable.

"Paula was extremely intelligent, but I was aware that I was leaving traces of infidelity in the digital world, on social media," says Greg.

He said he made jokes over a period of time pointing to her "obsession" with social media, making her feel that she was suspicious in an unhealthy, even "crazy" way.

"I deliberately used demeaning language to make her lose confidence in her reading of the situation, of my infidelity. She was 'paranoid', she was 'crazy', she was 'full of drama'.

"I'd say this all as jokes. But they would build over time, and she then started to believe."

The desired effect was achieved. Paula, who had suspected his infidelity, began to wonder aloud if perhaps she had been wrong to doubt him, if her judgement had left her. While she still had her doubts, Greg says she had started to question herself and apologised for suspecting him, vowing to spend less time on social media.

"Gaslighting as a term has been overused," says Dr George Simon, psychologist and author of international bestseller In Sheep's Clothing: Understanding and Dealing with Manipulative People.

"Gaslighting is when you know in your gut that you have a situation read right, but the other person is trying to convince you that you have read it all wrong. If this happens over a period of time one's sense of reality slowly erodes. There is a scale to gaslighting, from lying and exaggerating to controlling and domination. Greg was on the less extreme part of the scale but definitely on it."

Another tactic Greg used was to discredit other women. Some were women Paula had never met - the women he was cheating on her with. Others were Paula's own friends.

"I'd construct narratives where these other women, the ones who could reveal my behaviour, were women who couldn't be trusted, where they were liars.

"And despite Paula's better judgement, despite saying she was a feminist, she would then trust me and take a dislike to women whose version she would now no longer believe, even if she did meet them and found out they weren't these terrible human beings I made them out to be.

"I was isolating her from those who would tell her the truth."

After Paula, Greg embarked on a series of other relationships. He says that the women came from a variety of backgrounds and had different personalities. The pattern continued.

"There are two traits that people - and we must say people as men are also vulnerable - who are prone to being gaslighted share," says George Simon.

"One is conscientiousness. People who have a conscience, people who generally do the right thing and are trusting, because they are trustworthy in nature.

"The other is agreeableness. You want to treat people well and get along. You don't want to unnecessarily rock the boat in your relationships."

Nicole spent years living with a charming man, but she always seemed to be doing something wrong. Eventually she began to realise that it wasn't her that was the problem, it was him - and when she met one of his previous girlfriends, Elizabeth, everything made sense.

Read more: Gaslighting: The 'perfect' romance that became a nightmare

For Greg, there was a third quality that the women he gaslighted all shared. They were all intelligent and successful. Intriguingly, he says this was a key factor in how receptive they were to being gaslighted.

"I've dated a doctor, an engineer, a well-known social media personality.

"From my experience it's not true that it is vulnerable or insecure women who are susceptible to gaslighting. These were successful women but that came with a perception of what they thought a 'successful' relationship should look like and they shared that. They gave me a blueprint to what they were looking for in a man."

The women, he says, approached relationships like they did their careers. With a checklist of qualities, often from relationships depicted in films, and high expectations.

They wanted stimulating conversation peppered with attentive charm and humour. They were also looking for men who could match them in their success - men with impressive careers who also owned property and had financial security.

This kind of checklist narrowed the field of suitable men considerably, he says, and made it easier to play to their desires.

"When you are gaslighting, you see the narrative that the other person wants the relationship to follow and you then go about setting how that fits in with what you want. As a result, you do little things over an extended period of time that increases the likelihood that the partner will accept your narrative over their own.

"In my case, I have never been aggressive, violent, issued threats, or blackmailed anyone. There has literally been nothing stopping any of these partners from telling me to get lost. But none of them ever did.

"So for a long period of time I didn't feel like the villain."

But now, he says, he is aware of the consequences of his actions.

"These women were intelligent and I felt that if they wanted to, they could have questioned the narrative I was spinning. But now I'm aware that is a flimsy argument where love is concerned.

"I wanted the experience of multiple partners and the ego boost that came with that, so I justified my behaviour to myself for years.

"I guess, as a lawyer, I was able to explain away discrepancies in my story to girlfriends and convince myself that I wasn't a bad guy."

Some tactics of gaslighting, including isolating the victim from sources of support and depriving them of means needed for independence, could fall under the "Controlling or coercive behaviour in an intimate or family relationship" section of the , in England and Wales.

But controlling or coercive behaviour is not a crime in Canada, and the same is true in many parts of the world.

Recently Greg told a friend about his behaviour and his friend confessed that he too had been a gaslighter.

"My friend is a writer, so I guess he's also good at constructing narratives."

He says that if there is one piece of advice he would give women who are being gaslighted it's to speak to a male friend about it.

"Women in friendships often tell each other what they want to hear. Or if women do have searingly honest friends, this friendship seems to come under strain when one woman enters an abusive relationship.

"For some reason women seem to accept honesty better from male friends than female friends.

"I was wary of the male friends of my ex-girlfriends. They could often see through my behaviour and good male friends don't allow a friendship to break."

Greg says there was no one thing that caused him to seek help to deal with his gaslighting - he just grew weary of his own behaviour.

He wouldn't say he's cured yet, but he hopes he's on his way there.

George Simon says whether Greg can be cured or not depends on what type of gaslighter he is. There are two types, he says.

"Some individuals have learned these behaviours from early childhood experiences. Their manipulation rose out of some kind of personal pain and this is how they operate in the world. They developed a strategy to cope in life that was borne out of some trauma. There is hope for those individuals.

"Then there are the narcissists. The ones that have no belief in anything bigger than themselves. There's less hope for them and any change usually involves a huge, life-changing, catastrophic reckoning that shakes them to their core.

"And that may never come."

Greg and Paula's names have been changed

Illustrations by Tom Humberstone

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