Relationship red alert: you and your partner may have a love tighter than Jen and Brad's and still not necessarily be immune to infidelity. “The idea that loving your partner is all the insurance you need against having an affair is a myth,” explains Shirley Glass, author of NOT “Just Friends”. “There are good people in good relationships having affairs.”

Sounds scary, right? Relax... there is something you can do. Understanding the common causes of cheating and knowing the danger signals can give you the insight you need to pre-empt potential prowling – by you or your boyfriend. Read the straying-susceptibility questions at the start of each section and tune into the warning signs that you, or your partner, may be tempted to cheat. This cheat-prevention handbook has all you need to know to learn how to keep your twosome faithful.

Women Cheat Because...

They Allow Friendships To Go Too Far

• Do you constantly talk with your guy friend about each others' sex lives?
• Does he know all the details about you and your boyfriend's intimate moments?
• Do you often fantasize about having sex with a male friend?

“One of the reasons young women may be inclined to cheat is that they fall in love with a man they are friends with,” says clinical psychologist Dr John Gottman. You develop warm feelings for each other over time and eventually one night, whether you have had a fight with your boyfriend, or maybe a bit too much to drink, something happens. And because male-female platonic relationships – whether they're between co-workers, university students, or even a boyfriend's friends – are normal these days, there are tons of opportunities to cross the line from having a crush to cheating.

Making sure you don't takes common sense and willpower. The bottom line: even if you're happy in your relationship, you will find other men attractive, so put a stop to any randy possibilities before they even start. Instead of flirting with disaster, think about whether a little romance on the side is worth potentially wrecking your relationship. If you're not prepared to blow your current coupledom, lower the flirt level of your platonic friendship. Don't bitch to him when your boyfriend annoys you, skip the graphic discussions of your sexual preferences and don't be the last two customers to crawl out of the bar on a Friday night. Simply avoiding these sorts of sexually charged scenarios will keep temptation at bay.

Their Partners Don't Live Up To Their Expectations

• Do you have a mental check list that a boyfriend must meet?
• Do you freak out when you fight with your boyfriend?
• Are you aware that you're not as infatuated with your boyfriend as you once were?

“Women strive for protection in their relationships – sometimes to the point no one could live up to their standards,” says assistant professor of psychiatry Dr Scott Haltzman. Women who are sane most of the time, can be seduced into thinking that a solid relationship should be totally fight-free and that there must be men out there who fit into the Mr Perfect profile.

But if you bring your expectations back to earth, you can curb a cheating impulse. Flash: the hot guy you met in Italian class who seems perfecto? Get to know him amd you'll probably find out he snores, or his feet stink just as much as your boyfriend's do. So, instead of trying to upgrade your romantic reality, reignite your infatuation by looking at your boyfriend's flaws as a basis for a deeper bond. “As long as there are more pros than there are cons, the only way to grow closer to someone is to cope with his good and bad points,” says Haltzman.

They Feel Devalued By Their Partners

• Has your boyfriend stopped giving you compliments?
• Do you flirt with a guy just to see if he'll ask you out?
• Do you feel starved for affection?

In the early days of your romance, your boyfriend probably gave you enough random flattery you felt like a goddess. But after the initial love buzz wears off, many women feel neglected... and may seek out an easy ego boost from other boys. “It's exciting to get attention from someone other than your partner,” says Haltzman. But if you need to kiss that gorgeous bartender you've been watching just to prove you're a hottie, you have a problem.

We're not saying you have to write off the entire male species. Just limit yourself to innocent flirting, explains Haltzman. If you're out with girlfriends and a pack of boys come over to your group, it's OK to talk to them – just don't get deep with one single guy. If you do get into a conversation, work in a mention of your boyfriend before he asks for your number.

They Want To Punish Their Partners

• Do you tell your boyfriend when you're angry with him?
• Are you in a relationship rough patch?
• Do you think your boyfriend has cheated on you?

When your boyfriend does something that pisses you off, it's only human to want to get back at him. Unfortunately, a lot of girls tend to skip the confrontation and choose cheating instead.

Women who kiss and tell often use infidelity as a way to communicate relationship problems to their partners, says Dr David M Buss, author of The Evolution of Desire. Others choose to say nothing and simply derive satisfaction from knowing they've done something that would hurt him. So, next time you want revenge – whether it's after an argument or because you suspect he has strayed – don't jump into bed with another guy. Instead, meet up with your girlfriends and let off steam with them. If you still have a gripe with your partner the next day, “Initiate a chat about why your angry,” says Glass. Spell out what's on your mind and what you think would solve the problem. Males respond best to direct communication, so by being upfront, you will boost the odds fo setting things straight.

Men Cheat Because...

They Meet Hot Women At Work

• Does he often go to happy hour with colleagues?
• Does he spend a lot of time working with one particular woman?
• Does he work late nights and weekends?

Corporate culture can be a breeding ground for extracurricular carnal activities – especially if he works crazy hours, or likes to knock back a few beers with good-looking colleagues. “Even men who aren't of the philandering type will often wind up cheating with someone from work,” says Glass, who reports that 62 per cent of the men she counsels who have fooled around, did so with a co-worker.

The key to keeping him from grinding at his daily grind? Insert yourself into his working world. “Take an interest in what he does,” says Buss. Ask him about his big projects, or let him vent after a hellish day. Also, go with him to work functions, meet him and his colleagues for after-work drinks, or pick him up at the office when you meet for lunch. “That way, the predatory women he works with will know you as a person, not a faceless girlfriend whose feelings don't count,” says Haltzman.

They Like The Thrill Of The Chase

• Was he a player before you met?
• Did he pursue you aggressively when you first started dating?
• Is he a risk taker?

Some guys, especially the excitement-craving type, find that the constant stability of a relationship can feel like a straitjacket – and they break out of it by cheating. “Men will often start affairs because they're titillating,” explains Buss. “Guys like a challenge and having a girlfriend who's always unavailable becomes boring.” But if you re-create the sense of adventure within a secure relationship, his hunter instincts will be satisfied.

For starters, don't give him too long of a leash. If you're upset he cancelled your Friday night plans, don't just let him off the hook – tell him you expect him to make it up to you. If he calls when you're on your way out to meet your girlfriends, tell him you will speak to him later. “Even after you're an established couple, give him the chance to chase you,” says Haltzman.

The Sex Has Fallen Off In Frequency

• Is he always the one who initiates sex?
• Does he seem annoyed when you turn him down?
• Does he only say, “I love you” during sex?

As completely confusing as guys' behaviour might sometimes be, one thing is clear: if guys don't get enough bedroom action with their girlfriends, they're going to look for some on the side. “When a woman starts to pull away sexually, the man feels rejected and unloved solely because of being denied sex,” says Haltzman. But that doesn't necessarily mean that they're a bunch of horn dogs. Men actually use sex to convey how much they care about you, which is why they're more prone to use the L-word in bed. “Within a relationship, sex is a way for men to express and receive love,” says Buss. So when the physical intimacy between two people takes a nose dive, the man feels a dip in the emotional intimacy too.

Keep your sex life so sizzling, he won't have any libido to spare. If you notice that he's always the one to make the first move, make sure you take the lead sometimes. And be open to some erotic experimentation. “Guys want to fulfil fantasies with their partners to make the relationship closer,” explains Haltzman. So ask him what's on his dirty mind, tell him what's on yours and then satisfy each other's imaginations. “The more he shares with you sexually, the more solid his loyalty to you will be,” notes Buss.

- Rose Martelli