I'm sorry about America, she sounds like she was a beautiful girl- but try not to feel too guilty. Just think of all the bettas you have already given good homes, and the all the ones you undoubtedly will in the future. You can't save every one, there's just too many, but you've already done a great thing by loving the ones that you have!
I think I will feel the same about going to Petsmart, now that I know there is virtually no way I can get another betta, at least not until I am out of my dorm. It's just sad sometimes, and we want to take them all home- but I try to pour all the love I feel for the animals I can't bring home into the ones that I have.