I don't even know where to start with what is going on with Gus. If you love him like you say that you do and he bring so much happiness to you then you need to find a way to get him the necessary surgery that he needs. Whether that is through a lone, Carecredit or surrendering to a rescue it is your
responsibility as his owner to do whatever it takes to make him healthy. I see that your a nurse~what would your thought be if someone were to refuse treatment for a treatable illness.
If you do nothing he will die........that is for certain. It will be a slow and painful death.
*I also looked back on your other posts and I would advise against taking Gus on 3 mile walks while he is suffering from a shunt. His little body does not need any more stress. The aggressive behaviors might also be due to his illness. Please make sure that you address his flea issue as well. This too is putting additional stress on his physical health.
Please keep us updated.