I want to tell man's wife of affair, how do I build the evidence?

[Somersettler]

My best friend (F47) has been having an affair with a married man (M51) for 7 years. He has ruined her life while she has waited for him to leave his wife. My friend has neglected her family and friends in favour of him, and has never been interested in any other serious relationships with other men because of him. She's lonely, and turned to drink to ease her unhappiness. I think she's been unhappy for years because of him.

He has been stringing her along with excuses as to why now is not the right time to leave his wife, says he will eventually, says his relationship with his wife is dead. All the usual stuff. Every 6 months or so she would find the strength to try to end the relationship. Usually when he broke her heart letting her down, not being there for her, or generally treating her like the bit on the side that she has always been. But every time she's tried to get rid of him, he has come crawling back with gifts, and nights away and has always managed to keep her hooked on him. I hate him for what he's doing to her.

Tragically my friend has recently been diagnosed with terminal cancer. My grief and sadness has turned to anger at how he's made her so unhappy for so long. He won't be there for her when she needs him, he's not going to be holding her hand when she's going through treatment.

I want revenge. I won't do anything to upset my friend but if my friend doesn't make it, I absolutely intend to tell his wife. He's got away with it for far too long, and he's taking the piss out of his poor wife. He doesn't get to go back to normal when my friend passes away. I want to destroy him.

The problem is I don't have any proof of their affair. If I tell his wife, he can lie his, way out of it.

So I need to start gathering evidence. What proof do I need and how do I gather it?

Do it, OP.
I would tell the wife. Why should he get away with lying to two women and treating them both badly.
He will probably be on the look out for another affair partner once your friend passes. He’s clearly unhappy in his marriage and his wife deserves to know so she can make her own decisions.
Seven years! What a bastard.

All of this

It is a myth that men who cheat are unhappy in their marriage. If he was really unhappy he would have left . He has been with op’s friend for seven years .
He is perfectly happy having a wife and a bit on the side

Op’s friend will be dumped like a hot potato because of her diagnosis and he will replace her with another gullible woman

The OW's perspective (which you are supporting) is always fascinating to me, because it always shows a clear pattern of cognitive dissonance.

You wish to 'tell the wife' because you are sad about your friend's emotional suffering.

Yet you care nothing at all for 'the wife' (an autonomous human being, not just 'The Wife' to this man) who is the only person who is 100% innocent in all this. You care not one iota about what a revelation like this could do to her, her mental and emotional health, her physical wellbeing. Are you aware of what a life upending revelation like this can and does do to people? Not all people who are cheated go on to thrive.

You are in fact, chiefly concerned that she was not abandoned by her own husband in favour of your friend. Not left in the lurch. Not callously dumped by the wayside after years of loyalty just so your friend could be rewarded with what? A lying scumbag (and had he left his wife, you no doubt would be the bestie cosying up to both of them. Accepting him, no rushing to the wife with the full details then huh?)

YOUR friend, who you are here describing like a total victim with no agency, had a part in harming this woman, (whether she's aware of the affair matters not. He would have divided his affections, so even if unaware, his wife probably suffered) she has been a complicit partner in cheating and helping herself to something that she had no right to, and you knew and were aware of it for 7 whole years and you kept quiet and carried on your friendship without any moral qualms, and you now have the audacity to act as if you have some sort of righteous moral authority and high road and intend to rock up and put dynamite in this woman's life without a second thought for the trajectory the fallout may travel, or the destruction it might cause.

When people have affairs, the affair partner loses all perspective and sound reasoning ability and starts thinking in a very 'me' focused way. That's partly what keeps them reeled in, and any friends who get too sympathetic can fall into the same skewed perspective and off way of thinking.

I'd say this is what has happened to you. Heightened by the grief of your friend's imminent demise. She didn't listen to you and now you are being left with the pain of seeing her suffer emotionally in death. It's not fair to you either.

But it's for your friend to say anything. It's not for you. It will not be justice, it will not be honouring your friend in death, because it would not be something she wanted. It will be revenge. It will certainly not be motivated by concern for the wife. Neither of you gave a damn about her previously. And you will walk away potentially leaving a mess behind whilst conveniently shrugging your shoulders and telling yourself at that point that none of it is your lookout.

Your friend is as immoral as him.

Keep your nose out.

If the worst happens, and your friend passes away, why would you go against her wishes?
Sounds like you're very involved in all this. Maybe too involved? How have you put up with all the drama for seven years?
I'd honestly step way back. Does she ever ask about you and your life by the way?

Tell your friend what you're planning and go by her response if you must get involved.
But honestly, it's nothing to do with you.

Mind your own sticky beak. She made the choice. Must be desperate to cling onto someone who will never leave his wife

You leave it alone. Your friend knew he was married, she chose to be his bit on the side. No one forced her to do that.
Why do you want to make her life even harder, what good will come of you presenting evidence to his wife? Ultimately she close her life. She can still make choices. It's not your job to decide for her.
Now you support her in other ways, if you can't do that then you are no friend.
Edited to add and you aren't thinking about his wife at all. She's the only innocent party here.

There are five stages of grief. ..denial, anger, bargaining, depression and acceptance. Perhaps you’re in the anger stage of grief over your friend’s illness and the possibility of losing her.

This course of action doesn’t sound psychologically healthy for you: so I would park those thoughts. I hope your friend makes a full recovery. Her perspective may well change anyway now she is facing this new challenge. I would focus on being there for her.

Why don't you blame your friend equally? Or accept that this is what she has chosen? You are misdirecting your anger. In my experience all 3 parties, wife husband side piece after this long and at those ages know the score and build their own story to make it livable for them. He's probably going to scarper as soon as he learns her diagnosis so concentrate your energy on supporting her. If you contact his wife and bring all this out in the open and he chooses his wife your friend will 100% blame you. Unless you are actually the mistress in which case have at it you can't make things worse for yourself

Off topic but I love your username!

Don’t get involved. Your friend should never have started the affair anyway. We all have a choice!

It’s the expression I hate the most on this platform. Why not care for each other? I like living in a community, not living among a group of individuals who wouldn’t help me out if I was in trouble. Yes I’d certainly tell the wife . You don’t need proof, just ring her up and tell her. She’ll almost certainly believe you because the sincerity will be obvious

So sorry that your friend has terminal cancer, that must be awful to deal with. Your friend has chosen to be strung along with this guy, and your desire for revenge sounds unhealthy, what gives you the right to act like the moral police on this matter? Your friend knew what she was doing. You should stay out of it.

And what if the wife decided to confront the other woman? You know that often the wronged party decides to vent her ire in that way? Do you think that will help a person who is terminally ill? What will be achieved then?
The time has long passed for concerned friend to get involved.

He hasn’t caused the diagnosis. They BOTH chose to continue the affair. Revenge rarely delivers the relief it promises.

@WhatTheHellsGoingOn the man is a twat for deceiving his wife to cheat on the friend but how did you get to the conclusion he is a rapist ? Sorry if I read it wrong.

OP I would stay out of it. Channel your anger elsewhere

OP is only intending to tell if her friend dies.

@Somersettler I disagree, his wife should know. And stress is so bad for cancer, if he messed her around this time, you should tell his wife but anonymously. Why shouldn't the wife know, who is to say your wife is the only one, he may be putting their health at risk by sleeping around. If I was the wife I would want to know, im sure theywife suspect something but hes probably gaslighted as he is with your friend.

I think you should probably think about what your friend would want if she dies.

Would she want it to all come out?
Is she angry about the way she's lived her life?
Would she want him hurt?

She made her choices, maybe she's OK with them.

It's not really about what you want to do.

She would be better off supporting her friend. And, quite frankly, I think she might be tempted to contact the wife before then. She's over invested. And does not think her friend has mostly caused all of this.

Your friend isn't an innocent by stander. She gas knowingly been in a relationship with a married man for 7 years. She has chosen to be his side piece. She chose her poison. Your focusing on your anger and hurting him. You aren't considering the collateral damage. He has a wife and children. Where do they and their feelings come in this revenge? Fo you think your friend wants you be associated with all of this hurt and drama in her death? I think you need to mind your business.

She can be wishing ill on the guy and dreaming about revenge privately, while still supporting her friend practically and emotionally. Multitasking 😂

I don't see anywhere that she's considering blowing it all up while her friend is ill.

This isn't about helping. This is about anger and destruction.