I lost my boy at 7 years old to this cancer. I am so very sorry your pup has the same
Enjoy your time with him, each day now is a gift so make the most of them.
As for pain etc. I Don't believe my boy was in pain at the end, he became very weak and tired, lost interest in food. You will know.
There are some supplements you can.give that may help to minimize bleeds. One is Yunnan baiyao, won't hurt to try if you can find it
Again, I am so sorry.