Welcome, @neeny to the club that none think we'll ever belong to. I'm glad you've reached out for support. You'll find plenty of that here.
This is a safe place to ask what you want/need, but always remember, any advice comes from our personal experiences. It can't replace the advice of your medical team.
Going through cancer is tough, in any situation. I'm sorry to hear that your son is a long way away, and that your mother has dementia. I could be wrong, but I'm guessing no siblings, at least nearby, either. I'm single, with a close extended family, so had the support of sisters and parents as I went through active treatment, starting almost 4 years ago. People do genuinely want to help, so let them help in whatever ways you're comfortable with.
It's a safe place to vent, too, as you'll see on many posts. We're here to listen, and offer whatever support we can. Come often, or occasionaly, whatever works for you, there's usually someone around to answer.
Take care