This is fairly simple if you have read up on much with 'cheating women'. Most of it involves feeling 'wanted', and the excitement of 'forbidden' or 'naughty' sex. Hormones drive the behavior once things are done willingly, even if there was an excuse first. Once the first capitulation happens then many women simply shift the blame to the guy as in he 'forced' them to agree to the sex, and the continuing sex, and they simply side-step the fact that they are a willing participant who could say no, and choose not to. It's why so many women, even caught in the middle of sex, try to excuse it "it's not what you think" even if the dude was caught balls deep inside her.
In any event, to sum up, it's basically the woman giving in because she wants to on some level, and then continuing it because she wants to, using the excuse of coercion or simply not her fault. Any blame or remorse is side-stepped or minimized, and any guy she's with becomes a trivial person she loses connection and intimacy with as the new guy takes over.