Hello, and welcome to the forum! Unfortunately, this is a very common occurrence with animals bought from any chain store (Petco, Petsmart, Pets Supermarket, ect), as they usually buy their animals from animal mills that often capture their animals from the wild, or otherwise mistreat them. The employees in most of these stores don't know or care where they get the animals from or how they care for them, and often attempt to trick people into thinking they are easy pets to make more money, much like a car salesman. Also, never release any animal into the wild! Non-native species often suffer worse in environments they aren't adapted too, and suffer a long, painful death if not killed by a predator or disease. If the frog were to become established, they would have a major impact on native wildlife (Examples are Cane toads in Australia, Burmese pythons in the Everglades, and Domestic cats around the world), and cause declines on our native animals. Here are some videos to help you out to avoid dangers like that again:

https://www.youtube.com/watch?v=CPeN...Hu-DsOauXRMjkw

https://www.youtube.com/watch?v=stgN...Hu-DsOauXRMjkw

https://www.youtube.com/watch?v=VO8T...Hu-DsOauXRMjkw

And I am deeply sorry for your loss, loosing any animal or loved one is a very difficult obstacle to overcome.