Hi @LostHusband and welcome to the forum, sorry it is under such difficult circumstances..
My wife and I have been married for 18 years, we have 3 children 2, 10 and 12. Shortly before Christmas we found ourselves in a similar situation to you where my wife wanted to leave. Thankfully we have worked through that for now and while things are still tough we are working towards a more stable future with the help of a councillor.
My wife lives with Borderline personality disorder so most of our marriage has been ups and downs. Like you my wife is my best friend and my only love... last year she was quite unwell and spent a signiificant amout of time in hospital so after supporting her through this time especially but throughout our marriage being told it was over was a bit of a kick in the guts for me. I am far from perfect but everything I do I do for our family and to try and keep everyone safe and happy.
My response to my wife wanting to leave was that I am not going anywhere and we need to work this out. Thankfully when she asked her parents if she could stay there mum told her to go home and sort things out with me. That approach will not work for everyone I understand but it is how I responded. That and constant remindres that I still love my wife despite how difficult things can be. Not always an easy thing to say but it helps for us.
I say this respectfully and intend no disrespect towards your wife or mine, but living with mental illness is difficult at the best of times. When you mention all the things you are meant to change I think of all the things I am supposed to change and have changed to no avail, it can become a case of constantly shifting sands and movng goal posts.
I suppose the first thing to consider (and you dont have to answer here) is are there things that are reasonable for you to adjust and have not? Are there things you are expected to change that are not reasonable? And is your wife going through any particular crisis at the moment that may be clouding her thinking? (This may pass with some loving patience)
For a good part of our marriage I avoided conflict by working long hours, this has not helped us at all, now due to a combination of burnout for myself (I could no longer work and support my wife at the same time) and my wife being significantly more unwell, I am not working but in a primary caring role. All this additional time together and reduced income came with its own challenges initally. (Itnhas been 4 years now since I worked full time.
Would your wife be open to seeking a councillor, we are fortunate that we have a very supportive church and our pastor was able to recomend a very good councillor whom we have both been able to connect with.
I know my response has been quite broad but I hope that you cab relate to at least some if it. Happy to answer any questions where I can or just to be an ear. You will find everyone on the forum here very supportive, I have found this space invaluable.