You are certainly having a really tough time, it is hard to hear the commonsense part of your brain talking when you are feeling so low but hear it you should.
Of course those horrible words said to you are not true. Your son’s addiction is incredibly nasty and he isn’t thinking logically, rationally or with any empathy or thought for anybody else but himself. He doesn’t know how to empathise; it doesn’t suit his addiction to care for you but for all that (and hard as it is to believe) your son is still in there somewhere, the son who does love you.
You are possibly the closest target, the one he has leant on before and succeeded in turning to his addiction’s advantage – you will always be worth another try until he faces what he has become. I firmly believe that one day he will wake up and get the help he deserves.
I am glad you have left your phone turned off, in a drawer – you don’t need to hear his addiction spewing its false accusations, you deserve as much rest, care and patience as is possible at this time.
Hospital trips for radiotherapy and chemotherapy are very wearing and demoralising I know, I hope the treatment will soon be complete and your partner on his way to good health – you both deserve so much more.
Sending you both every good wish