I'm so sorry for your loss, Annie...
I am sure that little Bubbles appreciated so much for your love and care. Actually you already helped him so very much. Turtles hide their illness and pretend nothing happened when they get sick until they can hold it no more -- possibly little Bubbles was already in an extremely bad shape when you bought him. After all, not like his life in the store, you provided his last days with so much love that he deserved, and now he's in a better place where he no longer suffers. You should be happy and proud that you gave him a home when he needed one most, Annie. RIP, Bubbles.