It's done, let it go!
Sorry, I'm not one to cry over spilt milk. It is done, I empathize that it was a hard decision, but now the "guilt" is just self harming. Let it go!Aw, that's a bit harsh @BigBlackDog.
The OP hasn't just had to let her dog go, she has also got to face medical treatment that must be for something serious enough to have had to make this decision. Let's show some sympathy?