No one seems to be talking about this being a normal part of the stage of life you're in. The 40's are typically the most miserable decade in a person's life, and this is well documented. The major caveat to that is "I know I'm depressed and have been for the majority of my life" - which adds a different wrinkle. But that it's getting worse now is to be expected.

Some readings, which have been helpful for me (I'm also in my 40's):

https://www.latimes.com/opinion/op-ed/la-oe-rauch-happiness-...

https://12ft.io/proxy?q=https%3A%2F%2Fwww.theatlantic.com%2F...

https://www.researchgate.net/publication/327097311_You_Only_... (particularly starting at pg. 37)

Bottom line: this is a natural transitionary period. To make it successful requires embracing that.