This is a common life path trajectory for women. There are several variations. It is all really very simple. And as such, this post will not be long.
In type one, a women sexes up with alphas, gets knocked up, and has a baby or two, Since the alpha in most cases is not willing to marry her, or does not have the money to marry her, she needs to find a man who will provide her with resources. This would be the beta. Typically she acts all lovey-dovey until she gets the ring, and after that all bets are off. This type is often younger than the other type, as they need to find the beta provider sooner, rather than later
In type two, a woman rides the carousel for many years. Perhaps as Dalrock suggests, “She waits such that she leaves as little youth and beauty to her future husband as possible”. And once again, as the alpha has not bitten with respect to marriage, so she finds a beta-provider type to give her children and resources.
Perhaps the provider does not know what was going on, perhaps he does not want to know what is going on, and perhaps it may work out all just fine. But there is a high likelihood that the demons that are suppressed by such an arrangement will come forth eventually. And all, including the children will suffer.