Not much to add here, except yes, me too, I know how you all feel! I'm 46, only child with no immediate family other than mum (who's now 85), single, childess, jobless - my previously successful freelance "career", like many others here, has gone totally down the tubes.
Although I didn't live with her full time, I struggled to keep mum safe and well in her own home for 23 years since my dad died when I was a student. I'd say the dementia was coming upon her for at least the last 10 of those years, but she was (and remains) in denial and would not accept that she needed any help at home, which meant I gradually came to be running her entire life, minute by minute, often by proxy from 100 miles away - fielding daily, if not hourly, crises on the phone and ultimately having to go behind her back to liaise with GP, health visitors, social services and the carer I covertly hired to "visit" her a couple of times a week (which is the most she would accept without suspicion).
Following a year of escalating incidents, she finally had to go into residential care last September. I had to arrange all of it without her knowledge, let alone co-operation, and continue to do so. I have finally got her legal and financial affairs under control, but will have to pack up and sell her house on my own within the next year to meet the care costs. The house was burgled just before Christmas (fortunately nothing important was taken, but it has been an additional stress dealing with insurance, arranging repairs, clearing up, and having security equipment fitted). I spent Christmas alone in the burgled house in order to see to it and visit mum over the holiday. She knows nothing of any of this; when I visit (a 200-mile round trip at least every other week), she never remembers having seen me and is often aggrieved that I apparently "don't care", because I don't "stay the night" with her.
I was lucky to find her a place in a very good, civilised care home with great staff, good food, and pleasant surroundings. She refuses to have her hair washed or cut (not had it done since last July, when I struggled to trick her into her local salon) and has not bathed for literally years. She is now at least physically safe, has no responsibility for anything, and has people around to help and reassure her 24 hours a day. Of course she complains about the other residents (somehow she remains unaware that she's in a care home and rates the others as "not all there", while believing herself to be fine!). But her friends still visit, as does the carer once a week for my peace of mind, and I always make sure she has everything she needs. She will never have to do anything for herself ever again.
My life, on the other hand, is in ruins. Most of the time, I think I'm remarkably sane, considering. But if I stop to think about all the might-have-beens and compare myself with contemporaries who have families and successful careers, it is very hard to bear. It's not even as if mum appreciates any of it. Going through some old photos and letters in the house over Christmas, I was reminded of how she used to be - the "real" mum underneath the dementia; I realised how long it has been since she could relate to me in that way and that I had almost totally forgotten her as that warm, generous, kind and caring person. So much of her time and energy now is eaten away by paranoia and bitterness (often against those - myself included - who have done her no harm at all). That is perhaps the most upsetting thing of all. You could cope more easily with caring for a physically sick person, with whom you could still maintain a real, two-way relationship, and who, on some level, is appreciative of your efforts and at least co-operates and has some sense of your separate life.
All I can say to anyone reading this whose relative is still in the early stages, is please get some outside help before it's too late - for them and for you. They will never accept that they need help, so don't hang on in the hope of this; ultimately, you will have to make these decisions for them, so act sooner rather than later, to salvage at least some of your own life. I wish someone had said this to me years ago.