I know ringneck doves but I'm not too knowledgeable about Diamond doves, other than they are tiny and cute and very docile. I know my ringneck is very happy now that she has a mate, but they can be quite noisy as they coo to each other. If you are home and able to spend a lot of time with it then keeping it as a single would be ok but it probably would be happier with a friend that understands it, especially if it's in its cage for most of the day.