That is it…and more or less the reason I tell people when they ask me WHY I am “good” without religion. Because I want things to be a certain way, so I try to act a certain way!
Assuming she’s not just in this for a short-term fling, I’d also ask what she thinks the chances really are of him actually ever leaving his wife for her- I mean make her give you an actual percentage estimate, not ‘probably’, or ‘maybe’. And then get a percentage estimate of the chances that he’ll stay faithful to her after leaving his first wife for her. Ask ‘have you done any research to come up with those estimates? If not, why are you putting less due diligence into your relationship than work?’
Not really much chance for you to succeed, but I’d at some point give this a try.
This is heroic.
She would have to make three arguments. First, there is a preponderance of spiritual and social institutions regarding marriage. In the presence of these things, how are these concepts outmoded? Second, she would have to argue why these concepts, outmoded or otherwise, do not apply to her. Third, she would have to argue that these concepts are either irrational (impossible for their ends to be achieved in the presence of these concepts) or have been superceded by a new and superior rule that governs these kinds of relationships.
I would argue that she is immoral, not amoral, unless she professes to hold no moral positions at all. Does she think lying, cheating and stealing are allowed all the time, in any situation? Because that’s what she is doing.
As for what would get through to her, I got through to a friend of mine who was doing exactly the same thing by asking her if it would be OK for her father to cheat on her mother. By “got through” I mean that she broke down and cried uncontrollably. It still didn’t change her behavior, but she did acknowledge that the wife was an injured party, and the she (my friend), bore some responsibility.
Well, it is certainly possible for a person already married to meet another person and fall in love with them instead. The problem as I see it is in the cheating. That implies less a grand passion and more a desire to have a little action on the side; the real offence is not ‘stealing’ or ‘poaching’ a husband so much as dishonesty (and inspiring, aiding and abetting dishonesty in others).
The woman in the piece is I think fooling herself about her role in all this. This fellow is very likely not a “catch” so much as someone who finds her convenient. She is being lured on by promises. How much are the promises of someone whom you know is lying to their other romantic partner worth?
Actually… this is inspired. I’ve been in more than one bid/no-bid conference with her where she pushed PRECISELY this kind of analysis.
In any event, if she shies away from this, it will answer my own, internal, personal question of whether she’s truly believing what she’s spouting or she just found the most convenient rationalization for what she wants to so.
She will be forced to accept that limitation when her married boyfriend refuses to leave his wife for her. Or she’ll get an STD or unwanted pregnancy with this or another philanderer and demand marriage and, when the flavor of the week refuses to leave his wife, she’ll realize how important those concepts can be.
I agree with the other posters - no way you could have gotten through to her.
I have to wonder, though - she’s obviously justified away any moral wrongdoing in being involved in this relationship. Fine. But does the married boyfriend feel the same way - does he also think that marriage is a meaningless convention? I imagine he does not or he wouldn’t have gotten married in the first place.
As an aside, how does getting e-mails from her at 3 a.m. make her a driven worker? I’d imagine just the opposite - if she’s not able to complete her duties during work hours, she’s screwing around at work so much that she has to work at home. Or she has no life because she’s wasting her time with someone she can’t do anything with outside of whatever clandestine visits they enjoy. It’s not like he’ll be available for her to introduce around to her mom and dad. Just my take, since receiving those 3 a.m. e-mails are a pet peeve of mine.
You already know the answer to that.
Does it really matter whether she actually believes this or is just rationalizing? Even if she couldn’t give two shits about destroying marriages, she should have some sort of respect for herself. And before that sounds too trite, let me put it this way: if she’s going to look at it like work, would she stay at a job where there’s no future for her or would she move on to a job that would offer upward mobility or at least that she could talk to others about without having them look at her like she’s a leper? Kind of like being a porn star vs. a contract manager - you can talk openly about the latter, but not as much about the former, and you certainly don’t want news that you’re a porn star getting back to your family unless you’re 100% certain they’re going to be supportive.
In other words, why stay with some jerk who’s already demonstrated he’ll cheat and who she can’t introduce to anyone else when she could be with someone else - a single and available someone else - who she could spent time with outside of whatever little rendevous they’ve been having?
This gives me an idea around how to deal with this fro a business perspective. While it may be ethical to steal a client away from another business with a no fixed term contract (likely to have a simple notice period), it is unlikely to be ethical to execute the requirements of a business arrangement, without signing up to your own contract, and while that business is still contractually obliged to carry out 100% of their work through the original company.
i.e., while she perhaps could argue that she could poach the business, get him to cancel the original contract and establish a new one, she should not be sleeping with him, while he is still with his wife. That is dishonest and unethical.
Plus, it is very unlikely to convince the client that there is any need to change the situation, since he’s got two agencies working for him instead of one. Should she want to make her contract exclusive, she’s got very little bargaining power here, which does not make business sense.
My brother the hotshot genius geneticist got to the point where he could start his own company and he totally bought into the “business ethics are my ethics” thing. Wow, did he get weird. His favorite excuse for the most despicable things was “it’s just business.”
Haven’t spoken with him in years. His marriage has failed. I think he’s doing okay, but really don’t know.
She’s always been a very “It’s not personal, it’s just business,” kind of person.
Of course, in every situation prior to this when she said that, it was in fact business and not personal. Kinda destroys the meaning of the phrase if applied to this situation, and maybe I should have thought to say THAT to her as well.
Usually I’m pretty good on my feet for coming up with counter-arguments, but this whole discussion left me flat-footed and mumbling. Thus, again, why I came here and started this thread. 
I would ask just what her actual goal is in pursuing the relationship. It may be that this is just a kind of thrill ride for her. Just sex with a little extra thrill based on danger and rule breaking? Or maybe she just considers this some extra tail on the side? Does she want to pursue other sexual relationships simultaneously?
If that’s all she’s looking for, obviously she doesn care much about him, and you may as well give it up.
Does she actually claim to love him? Does she actually want to replace the wife in his affactions? If she wants to destroy his marriage, she could certainly find a way to do it. Does she truly want to break up his other relationship?
If she really thinks she loves him, you might make some progress based on the danger of harming him.
But I’m guessing not.
Could you tell her that her married lover signed a “non compete” with his wife? 
Is it possible that she is a driven career woman and she doesn’t WANT anything more than what a married guy can give her? Which still doesn’t make it right for her to do what she’s doing, but it would make it a lot harder to talk her out of it.
One can only hope this guy is childless. Does she think the situation is any different depending on whether or not he has kids?
I got married without any mention of any god, and as you well know, I’m an atheist, and you can tell her that claiming a marriage vow is invalid because it is religiously based is bullshit. When we got married exclusivity was a promise we made to each other. Unless she’s seen a written statement from his wife saying it is ok for him to mess around, she’s full of it. Plus, you know he is lying to his wife at least some times about where he is going and what he is doing. Forcing someone to lie must be unethical.
As for business, I don’t know contracts, but if company A has an exclusive contract to supply a product to company B, and decides to also supply it to company C for some extra cash, there’d be lawsuits a-flying, right?
She’s not in competition with anyone as the contract has already been awarded. She’s giving her services up for free knowing full well that she’s a redundancy.
And most businesses axe the person with the least seniority when there’s a redundancy.
That makes her a stupid business person.
For me the key words in the OP were that the guy is “quite the catch.”
Okay. There are people who dwell in a different realm, and who think all’s fair in love and war. There are women who are married to men who are known as good catches, and they’re aware of it and aware of the fact that they may be put aside for a trophy wife. Or another trophy wife.
(In my view, a really good catch is a man who won’t cheat on you. Among other things…)
Anyway, in circles I’ve known with mores like these, it is considered quite okay to go hunting for a spouse among those who’ve proven themselves as spouses, or anyway it’s okay from the point of view of the friends of the huntress. The friends of the wife will think differently.
If she’s angling for a divorce and becoming the next Mrs. Good Catch, it could happen. I’ve known it to happen. They’ll need a whole new social circle, though, and probably that part hasn’t sunk in for her yet. In these Good Catch situations the woman often considers GC’s social circle as part of the deal.
More significant than that, there’s a difference between business and personal realms. Sounds like this relationship is just another business deal. I doubt it has the meaning and emotional/spiritual aspect that most of us consider part of a truly personal relationship.
She’s not giving you reasons, she’s giving you rationalizations. Trying to argue with her will only give you a headache. She’ll have to see her mistake on her own. I feel sorry for the wife and (if there are any) kids.