You have to buy more than one so they won’t be lonely.
In 2008, Switzerland passed the Animal Protection Ordinance. Among the many sweeping protections for animals was a clause that made it illegal to own a single guinea pig. This is because they are social animals and they are considered victims of abuse if they are unable to interact with other Guinea Pigs.
It turns out that it’s not just Guinea Pigs that are protected by this law. A number of other social animals are as well.
The species that “must be kept in groups of at least two animals” are (for mammals) guinea pigs, mice, gerbils, rats, degus and chinchillas, and (for birds) Japanese quails, macaws, cockatoos, parakeets, parrots, canaries, estrildid finches and – of course – lovebirds.
If you read German and you like legal documents (and who doesn’t), here’s a link to the 2018 Animal Protection Ordinance document itself – das Tierschutzgesetz. Enjoy