Friend of a friend, who was married herself, had an affair with a married man. They met at her workplace, local hospital, he was a consultant, she's a department secretary. Let's call her Jean and him John.
John's wife had a long-term chronic illness, Jean has a teenage son as well as a husband. John tells Jean he doesn't want to be responsible for breaking up a marriage whilst she still has a child at home, so they'll keep it under wraps until her son leaves home/goes to college.
Affair carried on for a few years, and involved lots of shenanigans at work- think them nipping off for the afternoon and friends having to cover for them. Lots of disapproval and ruffled feathers with colleagues.
Jean's son, skipping games at school one afternoon, walked in on her and the guy whilst her husband was away on business. Expect that is a lovely lasting memory for the kid. He panicked and called his dad.
Dad/husband comes back from business trip early, arrives next day. Massive fight, she leaves for work so he storms round to John's house to batter have it out with him. He'd been suspicious for ages of how close she'd been with John, also whether a member of secretarial staff needed to go on overnight/long weekend medical conferences several times a year.
Finds instead John's unwell wife (she has MS). She collapses in hysterics, as she's been in denial for ages, having had her suspicions but as soon as she sees this man and the look on his face they are all confirmed her world comes crashing down (she knows who he is as it's a small community and there have been work events with partners invited). Jean's husband drives her to hospital a&e as she is having a panic attack and can't breathe.
It's the hospital where the cheating pair work (it would be, small community, only one for miles). So word spreads quickly, especially as loads of people have known for ages, it's been the hot gossip, some disapprove outright, some cover for them increasingly uncomfortably. Jean has tipped John off that they are rumbled.
Someone in A&E calls up to John to let him know his wife is there. John runs to be with his wife. Jean runs after him.
They arrive in A&E to find his wife and her husband. Massive scene ensues. John tells Jean it is over in front of everyone, as he can't leave/continue to hurt his sick wife. Jean's husband screams at her that it is over and that their son wants to live with him.
Jean goes to her mum's that night after work as she doesn't want to go home. Mum tells her she isn't welcome after what she has done (teenage son/grandson has been round at Granma's all day as too upset to go to school). She is told to go home and sort out her own mess, she'll get no sympathy from her family.
So she goes back and her husband is in pieces. Absolute floods of tears, can't believe she would do this to him, to her son, what are they going to do, he still loves her but he can't look at her, how can they live together, how can they sell the house (market was bad) etc. Pretty emotionally exhausting night.
Next day, everyone at work knows, knows she had an affair, knows she's been dumped by the fancy man, people are whispering about her in front of her. Over the course of the day it becomes pretty clear that John is avoiding her, he sends her email saying that his wife has made him breaking off all contact a condition of the marriage going on, and he can't leave someone who has MS, he would be a monster to do that (I think he should have thought about that before having an affair really). She realises she is at the very least going to get moved at work, if not get edged out all together, because of the pecking order at work he can't switch speciality etc.
So she goes home and her husband has gone to her mum's with her son, as he can't take another night like the one before and he's already in trouble at work for cutting trip short and taking a day off instead.
Jean takes an overdose. Teenage son pops in morning to pick up some stuff, finds her. Again, lovely for him. He calls ambulance, they go to hospital she works at. She has left a note saying she can't go on without John.
Anyway, she survives and she and husband piece their lives back together. She does get moved department at work. She finds it difficult to get on with new colleagues as they don't want to get drawn into anything. Her husband is very hurt now a bit suspicious at the drop of a hat- doesn't like her going away, going on nights out without him, seeing friends in the afternoon for coffee. It's not that's he controlling, he just gets really nervous and clingy a lot. So she finds that difficult.
All this happened before I knew her. She did befriend a friend of mine- someone, who like me, was relatively new to the area, so didn't know the back story. My friend, worked at the same hospital sometimes, but wasn't employed by the hospital directly and is only onsite sometimes, and being new, didn't know all the backstory.
So we three are out for a coffee one Saturday afternoon, and this guy walks in and Jen is like a cat on hot bricks. He makes a real point of coming up and saying hello to her as he leaves- she goes bright red and giggles. Me and the other friend are like "Huh?" And she says he is an old flame.
But about a month later, friend is at a hospital night out. One of the porters who she is on good terms with tells her to watch her back. He's a bit drunk so he tells her a bit of the backstory and that hospital gossip is that it looks like Jean and John are starting up again- they are nipping off a lot, been seen whispering together, going into,store rooms etc. Porter says friend needs to watch her back because Jean is already using friend as a cover story - "Oh, I'm going to meet Jean" when she's off for a tryst, and people, who like my friend even though she's quite new, don't want to see her/her employer get used (it's a charity who have a contract for some ward/cafe catering, always a lot of competition for the contract when it comes up, any shenanigans might tip the balance in the favour of one of the commercial competitions who always offer more but charity wins as more healthy options/profits go to charity/established working relationship).
So friend asks Jean about this and that's when all the above story comes out. Jean says she is desperately unhappy at home, husband is now suffocating. She can't stand it, so when John approached her again with a view to starting things up again, she jumped at the chance. The deal now is that he can't leave his wife whilst she is ill, but MS shortens life expectancy so it won't be long (not at all ghoulish). They haven't managed to go away together yet, they've just been meeting up when they can, will friend cover for her for a night away.
Friend is thinks to herself "err, not sure I'm too comfortable with that, this seems a bit messy to me" so decides to take a different tack. Says , look you can't go on like this, this is all so emotional. If you're really unhappy at home, I've got this big house all to myself, leave your husband, you can come and stay with me for a while. Think through what you really want to do before you do anything, maybe you'd be better with some time to yourself. You never got that before because you couldn't go to your mum's when it lol came out, maybe you need that time. Then depending on what you decide you can go home and make a go of it with your family, or stay here til you get on your feet and get your own place. But Jean doesn't want to do that- she just wants to stay in the marriage until John is free. She and husband have financial security together- he earns quite well and so she can afford a nice car, new clothes whilst they are together. If she had to rent herself or get a mortgage, she could do it but she wouldn't have the same standard of living. It'll be different when John is free- his wife will leave him the house, the wife has money too, they never had kids, he has a consultant's salary then pension, she'd be leaving for a more comfortable life.
Friend is a bit like "Huh? Oh well suit yourself...oh, is this about your son's,standard of living? Oh, ok, I get it I think. 
". And she says, "look, I'm not going to tell your husband what's going on, I'm not going to drop you in it, but please don't use me as a cover story, I don't want him pitching up,at my house in the middle of the night one night looking for,you and you're not here."
Every time me, friend and Jean are out, husband is always on the phone checking where she is. He wasn't like that before- he would call once, ask when she'd be back, not be checking where she was every fifteen minutes. So,I am a bit "Is everything ok? What's happened. Is he controlling/emotionally abusing you? What's going on?" So I get let in the loop. It's obvious Jean's husband can sense something is on again. There's one time I am round at friend's house for a natter and Jean pops in with a couple of dresses for friend to borrow, makes out that she's here for the afternoon with us and coffee and cake, then phones husband, tells him where she is, makes both me and friend speak to him on the phone to prove who she was with. Then gets changed into sexy outfit and scarpers. All this within 10 minutes of arriving. Friend is like "Oh god, she's off to shag John and we've just been the bloody alibi".
Fairly obvious what happens one Saturday night a wee while later. Jean's husband turns up at friends house about midnight. Jean is not there and friend is none the wiser than the husband about where Jean is.
Friend finds out Jean has been using her as the cover at work too, so decides it's best for the sake of her job to distance herself from Jean. I say "Well, I only ever knew her through you anyway, and this is all too messy for me to be honest".
And again, it all comes out in public, and again Jen is publically dumped.
I don't know if they are now on round 3 or 4.
But really, if you were Jean, wouldn't your teenage son walking in on you, or finding you in the midst of a suicide bid, be enough to make you stop? Never mind public humiliation and workplace shunning.
Sorry for the magnum opus, it was good to write that all down!