I'm so sorry for your loss. I'm sure Blacky knows he was greatly loved and will always be very much missed by the family. Make sure you let Louie know that Blacky had a very happy life and he is in a very good place now. The pain does ease.
Getting another guinea pig is a good idea if you are sure you can provide the level of care cavies need. There is an awful lot more to guinea pigs than most people realise, so many still offer just the basic care of a hutch, water and food, considering anything else to be extras. I'm not saying this applies to you, but it is important you understand just what having a guinea pig entails, starting with the fact that you really should keep two guineas together instead of a lone piggy.
I know you mean well, nonamian_girl, but I get the idea that Louie is a young boy. The family took Blacky to the vets maybe a little too late but at least he got some kind of treatment.
Thinking of you at this sad time, orbie. xx
