Will my rat be lonely now?

I had 2 little boy rats, 8 months old. Last night I had to have Ronnie put to sleep as he got cancer and pnemonia. I am so upset. Now worried about Reggie as he is looking for Ronnie and I think he will be upset on his own. Is it possible to give him a new friend, I'm not sure it's a good idea, i think they would fight? Does anyone have any tips of how I can keep him entertained by himself? He looks so sad. :-(