I know this is an old thread but yes, rabbits should be in pairs. I had a single rabbit as a kid (female) and we got another female. They tolerated each other but would fight a lot and we ended up only putting them together when supervised, then one died (coincidentally) and the other was much happier.
I then got a single boy rabbit years later who was a house bunny, he didn't seem lonely as such but we had him neutered and got a female and they got on well but the girl bullied him sometimes.
The girl rabbit got a serious illness and they had to be seperated for the safety of the boy and he was miserable. She recovered and we put them back together, she was slightly disabled and he was still brilliant with her. Sadly she died (she was still young, only 4!) and he literally was like a lost soul! We ended up rescuing another male who we thought might get on, and in actual fact the best pair we have ever had was two males!
Females tend to be more dominant and aggressive, males are friendlier and more laid back. My two are like a little gay couple - they groom each other, snuggle together etc. it's cute!