My heart is breaking for you
My best friend is going through this with her 10yr old springer spaniel. It is heartbreaking. She has made me promise not to let her be selfish and keep Mackay going when he clearly needs to be let go. I hope she knows when it's time. I think you will too.
I am so sorry you are going through this. I want to send you a HUGE hug, and let you know that we are all here for you if you need it.