Nanarosie, I understand your situation. A few years ago I had to take over the care of an aunt and uncle in an emergency when I already had demanding commitments to parents and grandchildren. I at least had ties of affection to my aunt and uncle.
There is no easy exit and the pressures of emotional blackmail are not easy to resist, but you must, otherwise you will have a breakdown, and that will make the situation even worse. In my case after 8 weeks of providing intensive daily care we hit a second crisis and my uncle and aunt were bundled, I can use no other word, into a care home. It caused them great distress for nearly three months and they would not see me for over a month but they settled and. although my uncle has since died I still visit my aunt every few weeks.
The practicalities. Grit your teeth and tell your aunt that you can only visit, say, once a month and call in Social Services. They have a statutory duty to do a Care Assessment, although they will do everything they can to wriggle out of it, especially when there is an involved relative. Speak to your local Age UK, they may well have a caseworker who can help you, I was such a volunteer caseworker for 10 years. Their online site has many helpful Fact Sheets including one on Care Assessments. But mainly, just continually remind yourself that your nearer relatives have priority and you simply cannot do everything.