Even though they're not traditional shooters, the Ratchet and Clank games are really fun. There's a pretty big genre difference in the games in the franchise, with generally the earlier games being more platform-ey, especially 1 & 2. A lot of the humor from the original trilogy still holds up today.
There's definitely some "unfun" parts in the games (giant mech fight from rac2 and the hacker from rac3 come to mind) but overall cozy imo. Some of the most unique and fun guns in any game.
If you're looking for strictly more shooter, check out Ratchet Deadlocked. There's barely any platforming and no mini games that I can remember, it's pretty much all shooting. NG+ makes it super cozy. It's really nice to play emulated.
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.