Hi - I think Im just about to go on the same journey. Im an only child aswell and my mum was diagnosed with it about six months ago. She lives 100 miles away with her partner which happened after my dad died (her, her partner and partners family never told me straight away).
Her bf (who's 80) had a fall pre xmas and really bashed his shoulder up - we've never been close as I resented them to begin with (long story) but he called me and said that my mum was quite bad and he was struggling to cope with his shoulder (and her obv). Anyway he went into hospital couple of days ago and after some calls/texts from her bfs daughters I went to see mum. I don't need to tell you what its like but about 3 or 4 times in the day (ive since tried to make sense of the few days and that's what Ive currently come up with) she was overly repetitive in q's and stuff and being really really worried about her bf.
Sorry, Im going on a bit.. I don't think that her and her bf will work out for too long after he get back from hospital. Mum hasn't got her own property (after my marriage ended (it gets worse) im renting a studio - also have 3 boys (2 are autistic/non verbal) so "I think" I haven't got even room for her even if I could.
I haven't got advice for you Im sorry, obv Im fairly new to the dementia scene (ffs) but wanted to say youre not alone I guess. Im pissed off/scared already after a few days so I can only imagine what youre going through.