Emotional adulthood

I recently asked a question about my partners depression, I am so affected by his moods, as you pointed out this is because I am thinking thoughts about the circumstance that make me feel anxious, sad, angry.

I completely understand this but i am struggling to apply it, I have let myself (for years) be so affected by his mood, if he’s sad, I’m sad and anxious because he’s sad, if he’s angry I’m angry and anxious about him being angry etc. Its a very ingrained behavior for me. (We both work from home in a small space so it can feel like there’s no escape!)

I have always been the ‘fixer.’ I take over, pay the bills, tell him it will be okay.

It feels like a huge leap to tell my brain his mood does not need to affect me, its my thoughts about his mood causing it.

How do I begin to step away from this thinking so that I can get to not going into auto pilot and absorbing the bad atmosphere/mood (with added anxiety for good measure!)

I really want to clean up my thinking around this as it feels as if it takes over my life.