( saying ) used to suggest that it is better to be in a group of only two people than have a third person with you as well
TWO'S COMPANY (, THREE'S A CROWD)
Meaning of TWO'S COMPANY (, THREE'S A CROWD) in English
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005