Dad in final stages small cell lung cancer

I joined this community awhile ago but haven't been able to bring myself to post until today. 

My dad was diagnosed with small-cell lung cancer that had spread to his bones, in March this year. He is now in the final stages. I live in Scotland and my dad lives in Canada. I have been supporting his wife with getting things organised, and supporting my dad emotionally through texting and Skype. Recently this stopped as he is no longer able to use his phone. I flew to Canada yesterday to be with him as he's deteriorating quickly.

I cannot believe how quickly things can take a downward turn. He was doing well, the chemo worked wonders and shrunk his tumours, and we were awaiting a scan in a few weeks' time to check how the radiation went. This past week he has deteriorated so quickly and an urgent CT scan shows the cancer has spread to his liver, lymph nodes, brain, and further into his bones.

It's horrible to watch what he's going through. He sleeps a lot, is in pain,  and his emotions are understandably all over the place. Yesterday he held my hand and quietly said "what did I ever do to deserve this anyway?" He's very confused and aware of that fact - he tells me that losing his thoughts and his words is the worst part. He doesn't like feeling that his "head is all messed up."

I'll be doing all I can to look after him in this final stage. Canada has legalised assisted death, and I hope that when it becomes unbearable for him that this will be an option.

This stage of the illness is the most terrible thing I've ever seen. No one deserves this and I can't imagine the strength the dying person must have to go through this.