AFBB is a common truism in RP but tbh, young professional women are starting to out-earn men. The term is starting to lose relevance but the phenomenon isn't.

In other words, many women who are done with AF still get with a 'BB' because he's safe and will follow her lead and never leave her first. But his income is often rivaled or dwarfed by hers. She may still enjoy his added resources but they are a secondary consideration. I've been calling this the "subordinate boyfriend."