To answer the first part, while we do require a closeness and sexual release, this hobby is definitely a luxury, not a need. There a lots of civvie ladies that do it for free, but maybe those partners don't fill certain boxes, so we fill those within the hobby. Like all hobbies, without endless disposable income, you save for the things that you want.
To answer the second part; Yes, I can remember saving for an encounter and I walked away like I just burned hard money for no gain. That being said, it's something where there is blame to be had. It just happens, where bad days or chemistry just creep into what you expect to be a great experience. Chalk it up to learning and move on.