It is rather a pity that people often keep a rabbit alone in the cage :( I am sure the rabbit isn't happy. They love having a friend to snuggle up to, like here:
Mind you, don't just go out and bring another rabbit home without checking with your existing rabbit. They might not even get along well. It is like having a stranger plonked into your bedroom suddenly. How would you like it?
Absurd as it sounds, we brought Blackie to the petshop with us, to make sure he liked Whitty, hee hee, it was like a blind date. And see how happy they are now :)