An update for all those who kindly contributed to this thread...
I stayed with my wife through all of lockdown, and spent much time with my youngest daughter. It was time well spent, and we managed to really get working on my daughter's MH. She still has relapses, but is generally doing well.
My wife spent most of lockdown railing against it, and moaning about how she couldn't go out and do things. Which is ironic, because she never went out before lockdown. In that time I tried to get her to change her behaviour, and explained that she needed to put some effort into our marriage only to be told that I'd promised to support her "in sickness and health until death is do part". She even suggested sending our daughter to live with other family members so that I could spend more time with her?!?
At the end of lockdown, I left the marital home. My daughter chose to come with me, even knowing that we would be homeless for quite a while. We sofa-surfed and house-sat and borrowed caravans and tents for 6 weeks. It was great, but also really hard. Finally we found a small property to rent and live there now. We are so relaxed and happy now. Even my in-laws have supported us as we moved onto the next stage of our lives. Only one person (my own mother!) has been unsupportive - due to her religious beliefs. I left with only a few clothes, and have been told that the rest of them will be sent to charity shops. Oh well.
My wife has carers from an agency in every day now. I believe that two of them have already asked not to work with her...
I made the right decision for me and my girls. I am so much better, and so are they. When I started this thread, it was partly as a contract with myself. I've stuck to it.
There are bad times, when I feel guilty. But not very many. And then I look at how well my daughters are doing now and even that guilt evaporates.
This forum is an important place, where we can seek support, and guidance, and even fair criticism.
Everyone here is an important part of my life, both in the past and going forward.
Take care, everyone, and love yourselves. You're doing great!