RIP to my Glass Catfish

Glass Catfish cannot live alone... I didn't do any research about him after I bought him back... this is my failure... already been 4 days he didn't eat any since I bought new pair of fish and put with him... maybe he knew other fish have their partner, but he alone... so he don't look well and stress... after this, I did some research... this fish must live in group... the fish shop boss said they can live alone... sometime cannot simply believe people ><... However... he leave this afternoon... RIP to my Glass Catfish... T.T