Sherry - I am very sorry to hear of this terrible news. We will continue to send Bonkers healing vibes and hope that you will have many more years with him. He sounds like he is a very special cat.
I have read about these that come from injection sites and that make me nervous about vaccinations. Our other cat Boots lived to be 18 or 19 (SO doesn't remember the exact year he got her) and he only took her to the vet when there was something wrong which wasn't often. But he never took her in for annual shots and while her health failed in her last years she was fine overall. She didn't go outside though, was strictly an indoor cat as is Midnight.
Midnight and I are thinking of you and Bonkers.