Yea, I mean, when you think about it, if you have a stark A-B dynamic, then that means one person fell in love under a circumstance where they were needy towards the other, highly respected and admired them, maybe even feared them some (at least their criticism or the possibility that they'd leave). For the hierarchy to change, all of that would have to disappear. It's hard to distinguish having all that depleted and not simply call it "losing the love."

Especially since the most submissive (the most obvious party Bs) are going to be those with an anxious attachment style. Most people I've met like that tend to think that the fear of losing someone is love. As soon as they feel too safe, or too empowered, it just feels like the passion is gone for them.