[chairman]

Snakes cannot feel lonely. They lack the portion of the brain associated with thought processes like that. They can feel stress related to fight/flight, which can be triggered by being housed with other snakes.

That all said, garters are one of the few that tolerate cohabitation well. You should stick to one species per enclosure. You also need to keep an eye on them when they're eating to make sure they don't both start eating opposite ends of the same meal- that'll result in an injured or dead snake.