I deal with this every day and in fact I don't usually live day to day I live hour to hour as I never know what will happen next as a day that starts or is going well can flip in a second to a very upsetting and stressful one. I have two sisters, one is a nurse, but they're next to useless. I've tried and tried to get them involved and begged for them to give one day a week alternatively, that's just one day a fortnight each and I'm not talking dawn to dawn as just three of four hours is a Godsend so that I can get a break and take my wife out but all it leads to is arguments between the two of them and slamming the phone down on each other and if one does come they do nothing in the house and in fact just make things worse and I have to deal with the mess they've created when we get back. When we do get out we're constantly on edge, looking at the time and wondering what we'll walk back into at home. Such is life. Me and my Mrs get a couple of hours here and there and maybe I get a holiday every two years and my God I needed a break this year.
Years ago a friend told me that looking after someone is a privilege and an honour. He really shamed me and I've never forgotten what he said. Plus I regard myself as a Christian and when I'm judged I want to say that I did my best for everyone involved. Some wont agree with this but it's my belief system and there are times when that's all I have. If I don't do this the alternative is some sort of home and I've seen how bad these can be and I've seen people go down so fast in them, IMO they're often a slow death sentence and if I push things down that path I don't think I could live with myself.
It's heartbreaking to hear someone ask the same question twenty times, to see them believe they have a partner and that they're moving in soon but not be able to say who that person is. It's just heartbreaking when they forget where they are, reinvent past events over and over again, allocate blame that just isn't there or suddenly become abusive but there are good times too but the bad times can be devastating as can the strain of doing it all. I have IBS, I get heart palpitations and stress and anxiety and depression and there's the effort of it all, being the first up and the last to bed every day and days lasting from 6am to midnight or 2 or 3 am. When we have a bad day I get immediate physical effects that can take weeks to get over and all this can come out of the blue when I think we're having a good day. For me it's just something I have to do for three reasons, there's no one else, I don't agree with putting people in homes unless it's absolutely the only/best thing for them and lastly and whilst my Mrs is understanding, I think it's the right thing to do.
I don't know what to suggest in your place Dave other than to look within yourself and make choices that you're most sure you can live with.