Rabbits are better kept in a pair or group because rabbits are social animals and they really do feel loneliness, which can lead to health and behavioral problems such as apathy and aggression.
Some people think they can replace that but nothing is better for a rabbit than a companion of their own sort.
If you want to form a couple, don't keep rabbits of the same gender. A castrated buck (male rabbit) and a doe (female rabbit) is the best combination; bucks will certainly fight after adolescence and does mostly have a love-hate relationship which also results in frequent fights.
A group of rabbits is also possible, then you should best try to keep the same amount of castrated bucks as does. This combination is more difficult and inexperienced pet-owners are advised to ask a shelter specialized in rabbits to help them in forming a good group.
A rabbit, kept in good circumstances will normally live about 8 years. Rabbits who are kept alone on the other hand, barely reach four years of age.