Most people are basically moral. Meaning faced with a moderate degree of temptation, they will still do the right thing anyway. There are some crappy people in the world that don’t ever experience temptation, because they have no moral compass and just do whatever they want all the time. Most people are moral… but not saints… everyone has their price where they become okay with doing evil.
For example, ask me to kill a kitten… and I’ll say no. I happen to like kittens. Ask me to kill a kitten for $100 and I’ll still say no. It’s just cruel to think about. $1000… ah… no. $1 million bucks to kill a kitten… and… well… how many dead kittens do you need?
So let’s consider how the morality sliding scale works with affairs. Let’s create a fake couple Anne and Alex and the third wheel Brad and watch the slide from White (morally good) to Black (full blown affair)
White – Anne and Brad know each other and nothing questionable is happening between them.
White/Grey – In this transition point, the first crossing of the line happens between Anne and Brad. Usually it’s simply a low key feeler thrown out from the guy to the girl. Something “non-serious” and easily disclaimed as an accident or no attempt to be offensive. Failure to knock the feeler back by the girl is implied acceptance of the advance to Grey.
Grey – This is the zone where Anne and Brad know that something inappropriate is happening between them, they don’t want Alex to find out about it, but it’s also reasoned as being “just flirting”, “not cheating”, “harmless fun”. Except it’s not really any of those and is being kept secret. At this point it’s an emotional connection and not physical.
Grey/Black – Anne and Brad kiss. This marks the transition into the affair being more physical. It may not turn into sex with the first episode of kissing, but it can escalate very quickly to sex after the first kiss. It’s a major hurdle to cross.
Black - Anne and Brad are now in a full sexual relationship and there’s a huge desire to hide it from Alex.
The idea for Brad is to navigate Anne through the scale of white to black at a steady pace, without stalling in any of the areas for too long, but not so fast that she hits a moral limit she isn’t prepared to break just yet. So he shouldn’t stall out too long for going for the kiss, but also shouldn’t go from introductory flirting to asking her to suck his dick either. (Try not to think of me as just having given advice on how to seduce someone’s wife, and more explaining how they do it.)
Now from Anne’s point of view…
White – Nothing is inappropriate, I love Alex. Brad is okay.
White/Grey Rejects Brad – I love Alex, Brad was rude.
White/Great Accepts Brad – I love Alex, Brad is funny.
Grey – I love Alex, but I’m falling in love with Brad.
Grey/Black Rejects Brad – I love Alex, I want Brad but I just can’t do this.
Grey/Black Accepts Brad – I love Alex, but when I’m with Brad I feel amazing, I can’t not do this.
Black – I love Alex, but it’s fading and I’m not in love with him. I’m in love with Brad and I’m starting to love him.
Importantly, if Anne rejects Brad at the White/Grey or Grey/Black transition points, there’s minimal chance she will tell Alex what happened. Most of the time he will never find out anything was happening. If it’s at the White/Grey line, there’s nothing to see and nothing to tell. If it’s at the Grey/Black line, all he’ll know is that she was a little distant there for a while, but then she stopped being a little distant. He quite possibly never notices anything was going on.
Far more interesting is if Anne tells Alex she’s been doing something inappropriate. This is always an ass backwards ultimatum and Fitness Test from her to him. It looks like a confession, but it’s far more than that…
Fitness Test angle first. Brad already knows about Alex, and has been making headway on Anne by indirect and stealthy means. So he does not want a confrontation with Alex. Alex however doesn’t know Brad is making headway on Anne, so he’s not paying particular attention to mate guarding Anne. So Alex is the sleeping Samurai, while Brad is the sneaking Ninja. So when Anne confesses to Alex something is happening with Brad, it’s like she suddenly flips the lights on and it’s all on…. Yo Samurai… there’s a Ninja…Why don’t you and him fight.
Whoever has the strongest overall male frame/presence will carry the day. If Alex turns into a spineless writhing blubbering weakling in front of Anne and weepingly begs her to come back to him… she’ll find a way to go back to Brad. If Alex suddenly reacts with controlled fury and seeks to defend what’s his, Ninja Brad will drop a smoke bomb and vanish.
Ultimatum angle second: Anne let Brad get as far as he did, because there was something lacking in Alex. Look I know that’s hard to hear, but it’s true. So not only does Alex have to puff up and scare Brad off, he’s also got to figure out what Anne is giving him an ultimatum about. She was prepared to risk the entire relationship by telling him about her thing with Brad. If she didn’t want to put the relationship on the line, she would NEVER have told him, she would have just broken it off with Brad.
The good news is that Anne does at least want to have a relationship with Alex… provided of course he fixes the problem.
The bad news is that when she told him about Brad, it was a fairly sanitized version of what really happened. Alex must always assume that worse things happened and find a way to divine the truth as best he can. If it was a case of she slept with Brad and then “gets away with it” by Alex taking her back without knowing, she’ll not respect him.
So Alex must immediately (1) get the other man out of the picture, (2) scare Anne half to death that he’ll possibly divorce her (she will fail to respect him unless he does that), (3) start fixing whatever structural weakness he has in holding Anne’s attraction.
And just to be clear, I’m not saying get in there and start trading punches… as tempting as that may be. I’m saying gather your information and find a way to get them not wanting to be together.