He is very controlling over her, and is constantly looking for her all over the ranch, needing to know where she is all the time. This makes Curley's wife is very unhappy with her life, and she hates being stuck on the ranch with no one to talk to. However, her loneliness is not so prominent in the book as it is in the movie, because she is portrayed very differently in each. The movie version shows her as being more intelligent and sympathetic, but also much more lonely.
Gary Sinise changed the movie version of Of Mice and Men to make Curley's wife seem more intelligent. He did this by adding small things into the scenes that are almost unnoticeable. One thing that he did was during a scene that he added where Curley's wife is alone with George in the barn, and she is talking to him. She comes into the barn and sits down on the couch, but also holding some sort of book in her hand, most likely a diary. In the book, she doesn't have a book when she comes in. This change is significant because it implies that she is very articulate and that she probably does a lot of thinking when she is alone in the house. Throughout the story there are scenes that show that she is by herself a lot of the time, and having a diary is something that makes sense for her to have. .
Another thing that Sinise adds into the story occurs in a scene that he changed where Lennie and George are heading back to the bunkhouse from Crooks's room. On their way, they run into Curley's wife. There, Sinise puts in dialogue for Curley's wife where she talks about how Curley got angry and broke all of her records. This definitely makes her character more intelligent because it shows that she listens to music. It makes her seem much more civilized and cultured, instead of just some girl out in the country living on a farm. In the book, this never happens. Sinise probably made this change to create more of a sophisticated persona for Curley's wife.