:( My little congo tetra died, now the other one is alone help?

I had two congo tetra that lived happily in their big 6 gallon tank. One of them died today, he was just upside down and still breathing but he wouldnt swim right side up. I moved him to a large bowl to see if there was something in the water that wasnt agreeing with him and he died. It was my first fish funeral and I cried a bit. Before flushing him I checked to see if he had any signs of disease but me and my roommate could see anything so we chalked it up to old age and shock. Now my one little congo is all alone.... I was wondering what should I do now? should I get him another fish or two? im worried that he will get depressed