Oh my prayers are with your baby!
one of my dogs was diagnosed with insulinoma about 4 years ago. i found out because she started having seizures and it turned out to be the cancer ( insulinoma ) anyway it had already spread and they said even with chemo they gave her 3 months.........i didnt do chemo, i wanted her last days to be home in a comfortable place, not hooked up to drugs that wouldnt extend her life or cure her ( i would have done it had it been a different type of cancer or outcome).......anyway...........i gave her vitamins and herbs and she had 2 YEARS more with us, at the very end when she started going downhill I just couldn't accept it........she stopped eating, was sooooo sick, i just couldnt deal with it, i kept trying different things and the vet talked to me and encouraged me to rethink euthanasia, finally my husband said to me, you really have to let her go , she is in pain, miserable, and sick.
so we made the choice to euthanize her, and i was able to say goodbye, hold her, and it was as nice of an end as i could have hoped for her, she was no longer suffering, i feel bad still that i think i let her suffer longer than i should have, but i am crying just writing this because the feelings are still so fresh and that was 2 years ago here.
Please also try not to question yourself, you are doing the best you can and you love your doggy, I know i should take my own advice because i did the same thing and i still do. its hard not to.
my good thoughts are with you and your doggy.