I go through a vast amount of feta. It is the queen cheese on my table, always present, and also my main one with my savory baking or salads. Feta is traditional cheese for my country, so I grew up with it, many types of it. My mom would buy many months worth feta and keep it in a brine in a huge pot, without putting it in a refrigerator. With high salt, feta is preserved perfectly. It really will not go bad for even an year if kept in the right salt concentration and if the cheese is fully immersed in the brine.
Here in the US, though, feta cheese many times has very little or no brine. Without brine, feta will go bad in a few weeks, even in a fridge. That was my first mistake I made when I moved to the US. I had to throw away tasteless softened feta after a few weeks. But I learned. I now buy feta either in brine in cans (Bulgarian made, for example), or only a smaller amount if it is in a plastic sealed pack. I don't spend time to make my own brine.
I use a lot of crumbled feta as well - for salads and baking. I do like ease of readiness to use crumbled feta.
Crumbled feta is sold with no brine at all in any store (which makes sense; it would just disintegrate and sediment at the bottom would become useless); so without brine it will go bad, get moldy - I've gone through that learning curve too.
I buy my crumbled feta from Costco, which is more than I need for my one use. My solution to that is just putting the cheese in the freezer. That way, I don't have to worry about it getting moldy or wasting it in case I don't use it soon enough. The freezer will preserve crumbled feta in its original condition, and it will thaw perfectly. I usually don't even thaw the whole pack; I just take what I need and quickly put the rest back in the freezer to avoid thawing the unused portion. If the cheese did not go through freeze-thaw cycle and is dry enough (no liquid added), it will not become single block of ice that will be hard to handle; it will stay as separate curdles if kept frozen all the time making it easy to scoop what you need.
You also can divide cheese in portions and freeze in Ziploc bags. Freezing works perfect for me. Hope this helps.