No-one can predict whether your partner is going to betray you by cheating.
But, thanks to research, we now know there are certain factors that predispose people to being unfaithful, relationship expert Tracey Cox wrote for Daily Mail.
Some of these are within your partner's control - like whether they have a history of infidelity.
Others aren't - their parents had affairs, they're good looking or they happen to work in finance (the most adulterous profession of all).
This list will make you paranoid if your partner ticks all the boxes - but it still doesn't mean they will definitely cheat.
As with any relationship advice, trust your instincts as you answer each of the questions below.
But if your partner does score highly, be aware they are more vulnerable to temptation than most.
Keep both your heart and your eyes open.
Were they with someone else when you met?
'Mate poaching' - stealing someone else's partner - is incredibly common in the US (and UK).
Three separate studies set out to find out if luring someone away from another results in a healthy, long-term relationship with the person they left to be with.
The answer in a nutshell is no.
Poached partners tend to be in more dysfunctional relationships, make less reliable mates and are less satisfied and committed than people who were single and available when you met.
The studies also show they're more likely to cheat and to have more narcissistic traits.
How often are you having sex?
Most people assume if they're still having lots of sex with their partner, it means they're not getting it elsewhere.
While low or no sex does make it more likely for your partner to cheat, men particularly often become hyperactive sexually when they start having an affair.
It's change that you should be on the alert for: if your partner suddenly wants a lot more sex with you for no apparent reason, chances are their sex drive may have been awakened by someone else.
Have they stopped watching porn?
A survey by Illicit Encounters, the website for married people looking for an affair, found half of the 1400 men they polled stopped watching porn completely while they were having affairs.
Other research has found people who watch porn and masturbate are less likely to cheat than those who don't.
Did either of their parents have an affair?
You would think that a child who'd witnessed a parent having an affair and being found out would make them less likely to cheat.
The reality is sometimes the opposite.
Watching the devastation affairs cause prompts our protective subconscious to ask: "Who would you rather be? The one who cheated or the one who's devastated by it?"
It's not a conscious choice but it does happen: the child grows into an adult who abhors cheating but finds themselves doing it.
Parental affairs might be common but their effect is still long-reaching.
Ideally, your partner would have happy, faithful parents.
Have they cheated before?
The 'once a cheat, always a cheat' belief does have truth to it.
But the crucial question to ask if your partner has a history of cheating is why they did it.
A true serial cheater has no moral compass and will often see nothing wrong with being unfaithful.
Other people cheat in relationships they aren't committed to or aren't happy in, others have affairs in retribution for a partner who cheated.
Find out the circumstances behind why they did what they did. Then ask yourself: "Is our relationship different than the rest" or "Are they in a very different place now than they were then"?
How good looking are they?
A Harvard University study (US) revealed a definite correlation between attractiveness and divorce, leading researchers to conclude that being good looking was "a relationship liability".
A relationship with someone attractive is definitely more vulnerable to threats than one with someone who isn't so appealing, especially if you're going through a rough patch.
Interestingly, how good-looking your partner thinks they are is almost as important as how attractive they actually are.
The more attractive we feel, the more likely we are to find infidelity appealing.
How much opportunity do they have to meet people and get away with cheating?
If your partner's straight and works in a same-sex office with little interaction with new people, they have low temptation and opportunity to play away.
The partner who works for a large company and has a job that involves constantly meeting new people has more temptation than others.
If they also travel for work, there are more opportunities to sleep with other people and not be found out.
This is also highly influenced by the following factor...
How much daily contact do you have with your partner?
How many times a day do you check in on each other and how do you make that contact?
If you're texting a few times throughout the day, with at least one or two phone calls as well, it's harder for a partner to get away with cheating.
We pick up a lot about someone's emotional state by their voice.
Having to explain why they're out of contact when they usually are is difficult and the simple act of receiving a text or ignoring a call from you presses all their guilt buttons.
The better you know your partner's routine and whereabouts, the less likely they are to think they could get away with cheating.
How close are you?
A disturbing fact is the majority of reputable studies have found the majority of people who commit adultery are happy in their lives and relationships.
A Rutgers University study found 56 per cent of men and 34 per cent of women who had affairs were happy with their partners.
So knowing your partner is happy doesn't mean they won't cheat but if you're in a very close relationship, you're much more likely to instinctively know something is wrong.
We are closest to the people who know the most about us and if your partner is suddenly sharing all their intimate stuff with someone else, you're much more likely to notice than a couple who don't communicate well or tell each other everything.
How well do you know their friends?
Eighty-five per cent of cheating is with a co-worker, with friends and neighbours not too far behind.
It's also true people are less likely to have an affair with a work colleague if they've met their partners: it's very easy to pretend someone's single if you've never seen evidence to the contrary.
The more of your partner's friends and colleagues you know, the more visible your relationship is to other people who may fancy them.
It's also more likely you'll pick up on any telling body language between the two of them or directed their way.
If you're well liked, friends will also step in to talk your partner out of any plans to misbehave if they're tempted.
How much do they drink?
Studies show men who drink no more than the recommended weekly total are 82 per cent less likely to commit adultery than heavy drinkers.
Women are also far more likely to cheat when drunk - for all the obvious reasons.
Excessive drinking makes us lose judgement, relaxes inhibitions and creates the infamous "beer goggles", making us fancy people we wouldn't be interested in sober.
If your partner drinks heavily with his or her friends or workmates without you around, this is a flashing red light.
Does cheating fit with their moral code?
I'm not for a minute suggesting nice people don't cheat - they do.
But if your partner gets upset when they see or hear about other friends cheating, it's a good sign.
There might be circumstances when they're tempted but it's a lot less likely to happen if they find the concept of infidelity distasteful.