Curley is concerned that his wife is cheating on him with other men. He leaves her alone a lot while he is working. There are no other women for her to become friends with, and the only company she has is the other men. However, because Curley treats her as a possession rather than a person, he always wants to know where she is, what she's doing and who she's with. He would feel much less of a man if she was flirting with the other men on the ranch, who he sees as socially inferior.
Curley runs around looking for his wife all the time because she has a reputation for running around on him. She is described as being better looking than Curley and Curley is described as not being much of a "man" for her. He is not very self confident and is always overcompensating for this by trying to domineer the other men. She is also extremely lonely and is not shy about telling men that fact. She is married to a man who works an awful lot and this gives her the opportunity to search for "company" from other men.