Felines are generally quite territorial creatures, and may even choose being alone over being in the company of other cats. (petsmagazine.com.sg)
Cubby enjoyed the company of other cats and started to put on some weight and his coat thickened. (tulsapetsmagazine.com)
If your cat enjoys the company of other cats, consider a companion cat as a house mate (but always do slow introductions to ensure household harmony). (cat-lovers-only.com)