What will my cancer death be like?

I have had an extremely rare cancer. I have undergone radiation but things are grim. I have been left with what is called "the world's worst pain" trigeminal pain (damaged nerves from radiation). I am on huge amounts of narcotics and opiods etc. Cancer societies both USA and Canada can not put me in touch with other trigeminal sufferers. It is like being hit by lightening dozens of times a day. My quality of life is at an all time low. I have lost all my teeth from radiation too. weight dropping. My cancer is not resolved and I have declined chemo. Brain tumour inoperable. I don't want the next 10 years or so of pain if I get them. Is there a humane way to end this? Is there legal euthanasia anywhere? And suggestions? I can't enjoy much anymore. No one can understand this pain its far worse then any major tooth pain or migraine. Advise?? My last son leaves home soon and I will be all alone 16 hours a day. I am scared. I hate being alone. I want to die quick and painless.