When a girl's hypergamous nature calls, one of the best allies is going to be her sense of doubt. Most girls aren't just suddenly going to cheat without having some kind of distorted rationalization for their actions.

You probably know popular rationalizations like: "oops, I drank too much", "you're an asshole", "You didn't gave me enough attention", "I thought he wouldn't find out", "wasn't ready to be serious with you", "you weren't exciting enough", "I just wanted someone better (more successful)". None of these are actual reasons for her cheating, but they are reason for her not feeling bad about the cheating.

She has a lot to lose. Her current man can provide her with a sense of security, stability, status, income, support, attention, validation. etc. Would she cheat, she would stand the chance of losing all of that and her reputation with it. She needs to be very secure that these resources will be provided by the other guy.

Especially when a girl realizes she has better options, her hamster is going to spin into overdrive, searching for the best possible outcome to the situation. That's when the shit tests are going to start. That's when you are constantly compared to the competition. Failing the shit tests is just proving that you are the worst option, while she is only looking for the best. At the same time, she'll also be shit testing the competition to figure out if they are as good as she believes.

The worst thing to do during these exceedingly more difficult shit tests, is to react weakly. This is the part were she can rationalize you as being "abusive", "controlling", "dramatic", "broken", etc. The more rationalizations, the less she'll feel bad.

Once made out to be the bad guy, there isn't much you can do. She has her army of friends and orbiters that will rationalize it all for her and tell her exactly what she wants to hear. Your past with her doesn't matter, everything you've done or have given doesn't matter. It's all nothing now and she won't feel any guilt about it all. In her mind, you will be in the wrong and you will have to redeem yourself (within her frame). Beta billy would of course take this to heart, and beg and beg and beg, because his biggest fear is his own thoughts and his self doubts. If she still has a n unfilled need for the poor sod, he can take on an orbiter role to be useful.

She spent her live learning how to play a good victim. As a man, you can never count on people picking your side. If you're close to the girl, she could talk this negativity behind your back and affect your reputation, which is one of the biggest things you want to avoid. The best way to avoid all of this is to never get in the situation (don't do mentally unstable people).

We here of course can see through this and see the hidden games. It's all power plays where people try to take control and get the most benefit. That's why it's so important to maintain frame while she's prodding you and throwing shit tests at you.

She needs to know that she needs you more than you need her. That you have more options than her, and she risks becoming the one who's dumped, instead of leading a break-up.

She needs to realize that consequences of messing her shit up are going to be severe.