Hi LT83,

You are not alone! I am sorry to hear all that is going on here - this is a quite a lot. A lot of people here will surely relate to your story of confusion, discovery, isolation, and uncertainty.
My SO is similar to yours on this point, I do not deal with rages on a regular basis. I deal with someone who has extreme black and white thinking - he cycles between idealizing and devaluing me. I do my best to depersonalize, but it can take a big toll on you, that is for sure!
He feels intense emotional pain and constantly breaks with me which has led us to have all manner of problems over the years, before I realized he has some form of mental illness.
I am sorry for the strong impact this has had on you with the depression and big weight loss! Last year the stress was causing me to have sudden weight loss, and then regain, and then lose again, not large amounts, but enough to be stressful. I am glad you have started therapy. If you keep posting here we can develop into an extra form of support for you as well, to bridge your time between those therapy sessions of you like!
Has her current affair stopped? You mention Narcissism and gaslighting, so I'm guessing she is not remorseful and making you feel pretty bad around all this? Is that right? I am so sorry, that is so upsetting and painful when our relationships get so off track like this!
wishing you peace, pearl.