Hello,
Firstly, only you know what is the right decision, follow your heart.
What ever decision you make, it will be very hard.
If you walk away, you have the knowledge that your best friend, partner passed away without you, if you stay, you know you will be in for a hard journey.
To be there for a dear friend regardless of what type of relationship (marriage, lovers, partners, friends), is very rewarding. To assist someone along one of life's hardest journeys leaves a treasured memory in your heart.
I just spent 12 months on the journey of brain tumours, I was from the day Pieter went to hospital and was diagnosed to being there for the day he took his last breath, and I would not change that for the world (actually I would do it all again, if it meant the opportunity just to be with him, for even 5 minutes). It was my decision to resign my job and become full time Carer, and I have no regrets. It was a beautiful time (at times hard, and sad), but the knowledge that I supported the one I love through the journey of cancer and death is very rewarding.
This is not for everyone, once again listen to your heart, you already know what you need to do. Believe in your decision, do not have regrets.
Yours