Robs are sociable little things and it is true that they prefer company. If you think your hamster is less happy without another hamster, then it is something you should consider. However, if he has been on his own for a while and got accustommed to his own space, he may not appreciate another male in his territory.

I kept robs as a child, and had a male and a female living on their own. They were perfectly happy all their lives. If you do keep a sociable rodent on their own, however, it is vital that they receive as much contact from you as possible. I have a rat whom I've kept on her own, and I devote 5 hours at the very least to her every day. A hamster shouldn't need quite that much attention, but in his waking hours you should preoccupy and interact with him for as much time as you can afford.