I went through the same with my dad -he passed away with my sister and I, by his side, at home. It was probably the worst thing I have ever experienced but I would not change a thing (other than if I could stop him being ill in the first place!). My dad was a fighter and he certainly did and whilst we were on duty looking after him (we pretty much moved in to his house and worked from there because it is very exhausting) I just knew the time had come. It was absolutely heart wrenching and i felt like i was in a nightmare that i would any minute, wake up from. I realised that this was the meaning of "heartbroken" and it is the only word I could find to describe how it made me feel. Empty and there is nothing that can replace the void. However, I think of the people that don't get the chance to say good bye the way that I did. You can step outside the door and never come back again and that is what I think of, everytime a part of that nightmare comes back. I think there are people out there who do not get the chance to be anywhere near the person or say their goodbyes. I feel it was a privilege to be present with my sister- all 3 people that mattered to each other. I was very close to my dad, like your son and i do miss him like crazy. When i do think about the end, i try to change the mind set and see it as an honour to be the last person in his life when he left this world, as he was the first person that was there when I came into this world (well, and mum!) I treasure the memories that have come from the special relationship we had and there is not a single person who can take those away. They will live on. When they say that the person remains in you-my dad was a rock for me when he was alive and I always strive to make him proud. I do not know if there is a beyond, or after life but I always think if he were looking down, would he be proud of me? I try to do the right thing by him, no matter what. That is where I feel I am "made of dad!" He was my role model and inspiration and I hope to carry that on in everything I do. Missing him is hard but it is hard to watch someone suffering and I feel he is at peace. No more cancer means no more suffering. I will learn to cope and maybe get a bit better day by day, because you have to for your own sake and sanity. Most of all, dad would not want to see neither myself or my sister suffering and certainly not because of his parting, he would want to see us continuing with life,  carrying on his legacy and being inspired- because he built us that way. I don't know if this will help but feel free to contact me if you want to reach out or whatever happens on this forum!!