I don't think you're a monster -- I think what you're doing is noble and deserves recognition. Often I have had to be a supportive friend in difficult pet health situations, so I absolutely know what it feels like.
However, I do question why you refer to Toasty as "it". I understand you're trying to distance yourself to lessen the emotional impact. However, if it were you taking care of her grandmother in her final days, would it be acceptable to refer to her as "it"?
I also do have to question why the final step is shooting the dog. I could see if you don't have funds for euthanasia, however there are a fair number of clinics and shelters out there that will do a free euthanasia if you explain the situation. I understand if that isn't feasible but I urge you to consider euthanasia.
Either way, I'm glad he's being taken care of in his final days. It's what every animal deserves, and it shows you care on some level, even if you are trying to deny that feeling. I hope you can both find some easing of tension in this incredibly stressful situation. Thank you for caring.
Chiming in here to say that animal agriculture is the #1 cause of deforestation, through clearing land for pasture and feed crops. The most powerful thing we can do on an individual level to reduce deforestation is to switch to a plant based diet, and encourage others to do the same. https://ourworldindata.org/drivers-of-deforestation