Dear Clarissa,
I'm so sorry you and your mom are having to go through this. Life sometimes seems such an incredibly cruel taskmaster.
Please read this article:
http://www.virtualtrials.com/btlinks/death.cfm
It is written by a Hospice organization specifically to prepare people - both those suffering end-stage disease and their care-givers - for the final days. I am sure the physical descriptions will be hard for you to read - you might even need to just skim through them, but there is a lot in the article that can help you get through the weeks and months to come.
Only you can decide about when it might be time to stay at home with your mother, but remember - you could have the rest of your life ahead of you with this supportive man, but once your mother is gone, you will not have the chance to regain what you have lost. Be sure to make the most of whatever chance you still have to hold her close to your heart. If your young man truly loves you, he will support your choice if and when you decide to stop travelling and stay at home with your mom for whatever time she has left.
Sincerely,
Tre