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Then he hired a 26-year-old secretary. She was to herald the unravelling of his life in the most spectacular way.
Fuelled by alcohol and intoxicated by the fact that this nubile young woman made it crystal-clear that she desired him, he found himself in bed with her after the office Christmas party. It was to leave him nursing the biggest hangover of his life: within six months he was homeless and estranged from his wife and children, and out of a job.
Last week, matrimonial lawyer Diane Benussi warned male bosses who unexpectedly hit it off with a female employee that they might have caught themselves an "office piranha" - a man-eating woman who preys on married, high-status men.
Torn assunder: Colin with his wife Ellen before his affair with 'Clare' caused his marriage to unravel
And Ms Benussi, who has almost 30 years' experience in the legal profession, sounded her warning after noting an increasing number of cases involving single women chasing the married fathers of their children for financial support.
Many such women, she says, join companies with a large number of male employees with the sole intention of looking for a partner. The office party then offers the ideal environment to trigger such relationships.
Ms Benussi's warning comes too late for Colin, who was divorced by his wife Ellen, 38, nine months ago on the grounds of adultery.
Many women will feel he got no less than he deserved for cheating on his wife, especially when she was pregnant. But he feels he became a target for seduction by a young woman whose behaviour after that initial liaison was both threatening and obsessive.
"Office piranha is the right terminology for her," says Colin ruefully today of the young woman he blames for ruining his life. "I was reeled in hook, line and sinker by a woman who deliberately set out to find a husband.
"She knew I was married and that my wife was pregnant, but she still targeted me for herself. She seemed happy to try to seduce me and then destroy my marriage in the hope that I would marry her.
"She came on strongly, and I was incredibly flattered. But now I have lost everything I held dear, and will regret the affair for the rest of my life."
But in hindsight Colin's affair was, he admits, of his own making, for it was he who interviewed and subsequently hired "Clare", then aged 26, for the post of secretary.
"She was slim and pretty with long hair and a vivacious smile," he recalls. "I defy any man, however happily married, not to notice if the woman sitting in front of him is attractive.
"Nevertheless, I deny I hired her because of her winning looks. She had the right credentials for the job."
However, within days of Clare taking up her new position, Colin was having lunch one day in the office restaurant when she sat down next to him.
Colin confesses he was flattered that such an attractive young woman had made a beeline for his table. But he says he simply put her friendliness down to a willingness to make a good impression with her boss.
He adds: "I wasn't looking for any affair or even a 'bit of fun'. My mind was always on my work. I held a high position in a blue chip company.
"Also, Ellen and I had been married for 13 years," he says. "We already had two beautiful sons - Joshua, now 14, and Andrew, nine - and Ellen was expecting our third child."
However, looking back, what is clear to Colin is that he was an easy target for any man-eating woman. "Ellen and I were going through a bad patch at the time," he says. "She was finding our two eldest sons quite a handful, especially as she was six months pregnant.
"She'd given up her job as a high-flying marketing executive to have our children, and although I had a good job - let's say it was a very healthy five-figure salary with perks - we had lost Ellen's salary but still had a hefty mortgage to pay.
"I was in line for promotion and was putting in longer hours to ensure I got it. Consequently, although Ellen was a wonderful, capable mother, the atmosphere wasn't always great at home."
Colin further admits he wasn't getting enough of the mainstay of any relationship (particularly, it would appear, for men); sex.
"Our sex life had taken a nose dive," accepts Colin. "It sounds terrible, but it made the fact that Clare fancied me difficult to ignore."
Of course, he should have paid more heed to his marriage vows and firmly told Clare he wasn't interested, but if he was willing to indulge in a little flirting, she seemed determined to pursue Colin.
"For several months, wherever I was at work, she seemed to be. I did find myself sharing some of my problems and she seemed sympathetic. My ego was flattered, but I tried not to encourage her. She even asked me out for meals, but I refused."
The office Christmas party loomed, and with Ellen heavily pregnant, Colin decided to go on his own.
It was a decision he was to regret. "Clare was there, we both had a bit to drink and we ended up at a hotel," he recalls. "I realise now I should never have gone on my own to this party. Clare looked wonderful and I could no longer resist."
By 4am the day after, however, and as Colin put his key into the front door of his home, he was already regretting his night of passion. "As soon as I glimpsed the Christmas decorations in the front room that Ellen had done with the boys I felt a huge stab of guilt," he says.
"Ellen was awake and furious. She'd been worried sick about where I was."
The next morning, Clare began bombarding Colin with texts and phone calls, and over the next few weeks pursued him with a vengeance.
"The texts said things like: 'You were good in bed', and despite my feelings of guilt, it felt fantastic to have a woman's attention again.
"With Ellen focused on our sons and the pregnancy, it had been a long time since I had felt appreciated as a man. So, despite the voice in my head saying I shouldn't meet Clare again, I did."
Having succumbed to the sexual flattery of the office piranha, Colin was foolish enough to agree to meet Clare secretly, and during the next six weeks they had a series of liaisons.
"When I tried to tell her it was over, she would beg me not to go, and cry. She threatened if I didn't leave Ellen and marry her, she would kill herself. Once, she acted as if she were carrying out her threat, running across the road and was almost hit by a car."
At the same time, everyone at the office was talking about Colin and Clare's affair. "While fellow managers would slap me on the back in a manly type of 'well done, mate' way, behind my back I knew they thought I was a fool," says Colin. "I was passed over for two promotions. It was terrible."
Many would feel Colin got what he deserved, but his argument is that he never made advances to Clare.
"I would delete Clare's texts but she sent them day and night," he says. "So it wasn't that surprising when Ellen confronted me one day. She had found a text from Clare on my phone - it had sexual undertones.
"At first I denied all knowledge. By then I had told Clare I didn't want to see her any more. But Ellen kept on at me and finally I confessed the truth.
"She was devastated. I tried to say it was just a stupid fling but she didn't believe me."
In early March 2004, Ellen gave birth to the couple's third son, Adam.
"Even then Clare was still trying to contact me," says Colin. "She seemed utterly heartless."
Eventually, a few weeks after the birth, Ellen told Colin she had had enough.
"She left, taking the children with her, to stay with relatives," says Colin. "I was furious with Clare for leaving my life in ruins."
At work, the writing was on the wall. "People were horrified I could have had an affair while Ellen was pregnant. Pressure was put on me to go, and I felt so humiliated and ashamed that I had no alternative but to leave."
But far worse than this, Ellen refused to let him see their sons.
"I missed them so much that I used to drive past the older boys' schools to catch a glimpse of them. I spent £7,000 going through the courts to gain access."
Today, Colin and Ellen do not speak, instead communicating about their sons through lawyers. Their home is on the market to pay for legal fees.
Colin has another job, although he says the affair has set his career back several years.
"Since this woman threw herself at me I've been a broken man. We had a good marriage, but like many men I was tempted - and now I am paying a higher price than I could ever have imagined."
