You can't make a relationship affair-proof, but you can certainly lower the chances.
Research shows choosing the right person in the first place is the most important factor in infidelity.
But how do you really know someone is a good bet?
Some things are obvious to steer clear of (the guy who openly ogles other women when you're out) but are there any more subtle signs that can tell you if he's likely to be faithful?
Happily, the answer is yes - and here's six of them.
UK sex expert Tracey Cox has revealed the subtle signs that your partner is loyal - from sharing a close bond with his mother to having long-term male friendships.
He sees his mother a lot
First, the sheer time commitment of regular visits and responsibilities leaves little room for the free, unaccounted for hours affairs need.
Second, he has an extra person to answer to. Not only does he have to lie to you, he must lie to her as well.
Mothers are notoriously perceptive about their sons and if she raised him to behave decently, she may spot behavioural changes and unexplained absences faster than you will.
Seeing his mother a lot shows he values family and takes responsibility for the people he loves: he has a strong sense of loyalty and duty.
Finally - and it's a good one - if he's close to his mother, he's likely to have respect for women as human beings rather than just sexual objects.
He's as desirable as you are
It sounds counterintuitive, but if he's punching above his weight dating you, he's MORE likely to cheat, not less.
You don't need to match physically, but you should both feel you're getting a good deal with what you bring to the relationship (wealth, power, intelligence, humour etc).
If your partner doesn't believe he deserves you, he'll feel insecure. Insecurity makes him search for proof he is desirable – wanting an ego boost is a prime driver behind lots of affairs.
The uneven power balance leads to low self-esteem which also makes him susceptible to flattery. Any woman who pays him attention and makes him feel attractive gets his attention because he rarely feels that way.
It's not unusual for men in this situation to sabotage the relationship (why not cheat if she's bound to leave anyway) or feel resentful and cheat on the sly to privately even the score.
He's the same person with everyone
What do you think would happen if you suddenly saw your partner in a pub, with his mates, without him knowing you were there? Would he be chatting to his friends...or chatting up single women? If his friends see a different side to the one he shows you, it's a bright red flag.
The version you see of your partner should be the same as the version everyone else sees. If it is, there's no mask. He is who you think he is.
He has long-term male friendships, and his friends really like him
First up, a caveat: we are the company we keep. If you can't bear his close friends, get out of there fast. But if you do all get on; friends are a treasure trove of information.
If they've known him since school, they'll have a very good idea of the type of man he is.
It's not just women who talk - men talk too - and the type of man who cheats usually also likes to boast about it.
If his friends are nice and like you, be alert for subtle warnings. Or not so subtle. I remember meeting a new boyfriend's mates at a party early in the relationship, and saying to his best friend, ‘Wow! Charlie’s really going for it. It’s only 9pm and he’s drunk already!’.
The friend looked me straight in the eye and said, ‘He’s always struggled with alcohol. Are you sure you want to take that on?’. Charlie was a raging alcoholic and that guy saved me a lot of heartache.
If he's a nice guy, his friends will be singing his praises to you. If they're not, there's a reason.
He has a hobby that's all consuming
Whether it's restoring vintage furniture, golf or training for triathlons, a man who is obsessive about his hobby has no room for a double life.
Affairs are high effort: it takes time and a lot of planning to live a double life. If he'd much rather spend his spare time tinkering about in his garage or at the gym, he'll unlikely to be drawn to something that takes him away from what he loves.
Even better if that hobby uses up any spare money he has. Hotel rooms, restaurants, gifts - affairs are costly. A man who is watching his cash flow will do the maths and opt out.
He lost everything by cheating in the past
The 'once a cheater, always a cheater' is true - unless something dramatic and drastic has happened to make him change his ways.
A man who lost everything because of infidelity - a wife he loved (people who love their partners also cheat), his children, the family home and respect of everyone - knows the price of cheating when you're caught.
It's devastating realising you've sacrificed all that was important to you for a few weeks of hot sex.
This is why this guy can be a safer bet than someone who has never cheated at all.