How is the second branch secured during a monkey branching?

Definition: can be done by man or woman. But Lets say a girl is in a LTR or similar situation with a guy. But she meets another guy who is a perceived "upgrade". Generally the sentiment is that the girl begins cheating either physically or emotionally on the first guy, and she starts building an intimate rapport with the second branch. She will basically start "checking out" of the first relationship. Meanwhile building a connection with the second. When does she finally make the jump?

Is it AFTER he tells her he commits. Or is just "she feels he may commit but never actually did yet" enough? Wouldnt that by definition, not be a secure branch? From what I know about women, theyre very paranoid of guys who make false promises or lead them on, so they tend to wait for real commitment via actions to know a guy is serious, so them ditching the first branch for a "I hope he asks me" is very risky.

Does the second branch and her committ to each other while shes with the first boyfriend? So for a short window she may be in two official relationships before ending the first
What if her second branch commits and shes interested but not ready to physically monkey branch? Does she leave him hanging on the commitment part because she refuses to be in two commitments at once without destroying the other?

Is there technically a period where she breaks up with the first guy, is single for like a day or two, then commits to the second, so she feels like she didnt technically cheat on him?

Real life example: I have a friend who is the second branch. He and this girl have been hooking up for the past 3 months, and shes always told him she doesnt have a boyfriend. He actually recently found her TikTok, and found a man commenting on her videos, he saw the profile and hes posting couple photos with her, and their commenting bf/gf type stuff in the comments. He got the impression they were breaking up or on the verge of it, so he asked to go exclusive with her, and she has not really "accepted" his request. Hes confused because shes been sending him many signals and hints for an upgraded status with him. This is how i know, because he asked for my advice...

My question is this: Is it because shes still technically with the first guy? Does a girl need to break up first before accepting the second branch's request? This is the theory i presented to him, but right now he thinks theyre done because she has not replied at all to his text and its been a day and a half. I told him that maybe she doesnt want to be in two relationships at once, and she cannot say yes right now, even if she wants to, but she does know you are ready and secure for the swing, and shell need some time, wait for her to answer within the week or want to hang out, and see how things play out.

Im really curious on how these things play out. I will never branch swing myself as a male, so im not able to put myself in their shoes and guess.