People who are alike often become friends or are together; if you are often with certain people, you may be their friends or like them. A proverb. Don't be friends with bad boys. People think that birds of a feather flock together.
BIRDS OF A FEATHER FLOCK TOGETHER
Meaning of BIRDS OF A FEATHER FLOCK TOGETHER in English
American idioms English vocabulary. Английский словарь американских идиом. 2012