Guinea pigs are social and herd animals which means they need to live with other guinea pigs. You should never just have one guinea pig because they will get lonely and bored , even if you give it attention most of the time that still doesn't stop them from being lonely. Good combinations are neutered males and one/more females, two females, neutered brothers only if they have been brought up together. Guinea pigs like to eat, sleep and explore together and if your guinea pig is by itself then its not going to show natural behaviours they would most probably end up depressed and bored.
By giving your guinea pig company they will show their natural behaviours like they would in the wild.
Bad combinations would be 2 aggressive boars and you should never have a rabbit and guinea pig living together because they have different food diets and guinea pigs can end up getting bullied by the rabbits and a group of boars.
Just think about it you wouldn't like it if you were on your own all the time, couldn't talk or interact to anyone.
Just think of your piggy's.