I think it would be best to keep 2 of the same gender,seeing as rabbits can have litter after litter of babies,if housed with different genders. I'm not sure..I think if the rabbit gets along fine without another buddy,then it can be left by it self. Thumper used to fight with other male rabbits,even though we didn't have a female.After his friend died,surprisingly,he's doing quite well on his own. If the lone rabbit seems to be lonely on it's own,you cold try getting a friend for it,though I could be wrong..
Hope I helped,I'm sure other people will have better advice. (I suppose if you neutered the male,or spayed the female,then 2 different genders could be housed together..)
