There is almost always one larger earner, and one larger spender. For this to be coming up, necessarily someone (or both) has to be overspending. If both are

There is almost always one larger earner, and one larger spender. For this to be coming up, necessarily someone (or both) has to be overspending. If both are low earners, and aggregate earnings are insufficient to cover the lowest set of available expenses, then someone (or both) need to be living in with their parents. Or they’re going to be homeless, or similar. Often; it’s one or both parties overspending on unnecessary expenses. In which case, splitting up almost always changes the dynamics so at least one of the parties can stay solvent. But there are infinite ways to screw this pooch, of course.