Should you tell your friend their partner is cheating on them? I wish someone had told me.

An ethical question packed with a punch: if you knew someone was cheating on their spouse would you tell that person? Truth can be painful to hear, but it is brutal to deliver to a friend, your boss’s spouse, a neighbour, a family member, to anyone.

A thankless position to be in, but I wish someone had told me. Dozens of people had first-hand knowledge for years about my ex’s chronic infidelity. Some knew me, others didn’t. But they sure knew of me. Any one of them could have used facts and sent me an anonymous note or made a call. Family members actually knew and could have told me, which is especially sad. It would have been a gift, jolting me out of the state of denial that I’d apparently taken up residence in almost from the day I married. As far as I’m concerned, everyone who chose not to tell me walked away from the scene of a wreck and that wreck, unbeknownst to me, was my life.

The very act of denial is self-victimisation. But it’s only after you have the information that you can stop whoever is doing it to you and what you are doing to yourself as a consequence. (My ex worked 300 miles away, so it was denial by distance in my case. But only up to a point.) Nothing was worth the years that I allowed him to convince me I was crazy for questioning him while I raised our children, washed his underwear, and sent his mother letters praising him for being such a wonderful husband and father. Someone stepping out of their comfort zone, providing some key facts would have been all I needed to confirm what I was hesitant to face up to.

There is an etiquette in these situations that I recommend. If you know the person being cheated on well enough, you should tell them in person, providing the details you know. Keep reminding them you are only telling them the truth because you honestly care and respect them; as sorry as you feel having to tell them, you would feel extremely sorry if their future was compromised by allowing the deception to continue. Also, as I know first hand, extra marital sex is unsafe, exposing people to potential health risk, if not affecting their mental well-being. (Don't even get me started on what cheating can do to family finances, job security, and other key areas of one's life, all of which I am now well aware of.)

In situations where you don't personally know the person, but have strong, first-hand knowledge, I encourage you to drop them a note, give them the details you do know. Tell them that you hope the information might explain suspicions they may already have and assure them that your only agenda is being honest. If they choose to ignore the information, at least you've done your due diligence.

My ex and the co-worker he was a having an affair with caused a scandal in their workplace. But in spite of the fact that a whole department went to HR to complain, no one thought to mention it to me. I had to read it on the Internet four years and a million tears later.

In either scenario ask them, "Down the road, five, 10, 20 years from now, wouldn't you be more upset, mad, even furious you'd wasted all these years in a deceptive relationship, especially knowing someone could have told you the truth?" Based on what I experienced, as well as some of my friends, the turmoil of living your life in a environment with a cheater is crippling.

Many feel that telling someone to be aware that their spouse/partner is betraying them makes the messenger complicit in shattering the marriage. Who wants to tell someone that the love of their life is sharing their time, heart, mind, and body, probably family income, if not intimate facts about the unaware spouse, with another person? (The person my husband was having the last affair with loved telling people about their relationship, what a loser I was and all their plans for a future together. I think I was nursing our youngest from a broken back at the time.)

What if you're wrong? It's not likely you've actually seen them having sex. But even an emotional affair, an office flirtation, is going too far and is just as hurtful as extra marital sexual encounters, as surveys have confirmed (Archives of Sexual Behaviour, 2007). And frankly, where it's smokey, there is surely a fire in someone's crotch.

I can understand the fear; I was put in this position a few months after I filed for divorce. One of my best friends complained about her husband's total change in personality, picking fights for no reason. I asked her if she suspected he was having an affair. I explained that based on what I'd just experienced with my husband, I now knew one of the signs that a husband is cheating is acting hostile towards his wife for no apparent reason, as if he is attempting to justify his wandering penis ("See how unhappy you make me?").

My friend was certain there was no other woman, "His first wife did that, he never would," she stated. The next day she called crying. It turned out he was cheating with a co-worker. He also lied about his first marriage; he'd been the cheater that time as well. When someone lies about extra marital sex, they lie about a lot of things: drugs, alcohol, money, their education, the list goes on. When I told someone I was divorcing and what the circumstances were, she was a prophet, telling me that as much as I think I knew, just wait, there's bound to be more. Holy cow, was there ever, years and years of more!

A business associate told me when he caught his wife cheating, he told the guy's wife. She was furious, absolutely certain he would never do that. A few weeks later she called my associate, apologised and thanked him. She had confirmed what he already knew, giving her the opportunity to head off her cheating husband from moving assets out of the country, as well as get the jump on a divorce she had more control over.

If anyone wants to know if someone is cheating, start with the phone bill. (Cheaters are incredibly lazy about tell-tale signs, like texting their lovers morning, noon, and night.) I could have saved myself years of feeling demolished by my ex if I had checked the phone bill that I paid each month. After I filed for divorce, I went back and found hundreds and hundreds of calls/texts messages between my husband and his partner in stupidity. Apparently they couldn't go to the bathroom without discussing it before, during, as well as after with each other.

Ultimately, not allowing the cheater to lie one more time, take one more year, month, or minute of someone's life is the best reason to tell them. Living with a cheater is damaging to the soul and the regret is overwhelming. Being a knowledgeable party, or even bystander to a cheating situation is inexcusable.

This post originally appeared on Divorced Moms, and has been republished with full permission.