HUGE HUGS
Oh, no! I am so, so sorry about the horrible news. What a shock. But you have made absolutely the right decision and have spared him any unnecessary suffering.
Please don't change anything in the cage (apart from poo patrols) and let Ozzy's mate Bruno have his cozy/blanket from his vet trip. Allow him to grieve and to snuggle into the smell until it fades naturally over about the course of a week or so. For once, it doesn't matter if the cage is getting grotty. Only clean the cage as normal if the companion is behaving like nothing has happened and will appreciate the normal routine to continue.
If Bruno is shocked and not eating - it is more common after a sudden unforeseeable death like a fatal heart attack or stroke, please step in with a syringe full; often it is enough for the eating and drinking reflex to kick in again.
True pining (giving up on life) is thankfully rare but you will have to brace for several days of Bruno being withdrawn.
Please give yourself time to not be OK and to grieve. Please seek free trained volunteer help from the Blue Cross next week if you find yourself trapped in one of the weird mind loops that can happen at the onset of the grieving process, if you continue to struggle to sleep and/or function for more than just a few days. All forum members that have come back to us have always given positive feedback.
Pet Loss Support
We are of course here for you for understanding community support, any questions and concerns for as long as needed.
Again, I am so very sorry that it has ended so unexpectedly and dramatically. Try to take consolation that you have spared Ozzy a lot of suffering and that he could make his journey to the Bridge while he could still have an interest in food and life and enjoy a good life to the very end.
But please also feel validated that you are obviously a very sensitive person and that your gut feeling about Ozzy was right. Trust in yourself; there is nothing wrong with your love and your instincts.