In what way is Curley lonely in Of Mice and Men?

As the son of the boss, Curley is alienated from the bindle stiffs, who avoid engaging with him out of fear for their jobs because the jealous Curley always suspects the men of flirting with his wife.

After Curley belligerently enters the bunkhouse, George warns Lennie that because of the way Curley has acted and how he has looked at Lennie, Lennie will have trouble with Curley and they will be fired. 

"Look, Lennie. You try to keep away from him, will you? Don't never speak to him. If he comes in here you move clear to the other side of the room. Will you do that, Lennie?"

Apparently, Curley is very high strung and possessive of his new wife. Of course, there is some justification for this anxiety over what his wife is doing or where she might be since there are no other women on the ranch and she is pretty and rather seductive in her actions. But, because he is always so suspicious of the other men, Curley cannot be friends with anyone. His tone of voice is always threatening to them, and he seems to be looking for a fight.
In Chapter 3, Curley steps into the bunkhouse and looks

...threateningly around the room. "Where the hell's Slim?"
"Went out into the barn," said George. "He was gonna put some tar on a split hoof."
Curley's shoulders dropped and squared. "How long ago'd he go?"
"Five-ten minutes."
Curley jumped out the door and banged it after him.

One of the workers named Whit says that he is going to watch what happens.

"Curley's just spoilin' or he wouldn't start for Slim....I like to see the fuss if it come off."

Later, Slim comes into the bunkhouse, his hands black with tar. Curley follows and apologizes to Slim, "Well, I didn't mean nothing, Slim. I just ast you."
Slim says,

"Well, you been askin' me too often. I'm gettin'...damn sick of it. If you can't look after your own...damn wife, what you expect me to do about it? You lay offa me."

Curley tries to apologize, but Carlson then injects his opinions, saying Curley should tell his wife to stay home. Letting her "hang around bunk houses" will soon bring trouble, he warns. Enraged that a mere ranch hand would talk this way to him, Curley tells Carlson to stay out of his conversation with Slim, or he can step outside with him if he wants. Carlson laughs and accuses Curley of being afraid of Slim. Moreover, he threatens Curley if he tries anything with him.

Clearly, Curley's quick temper is a problem for him. He seems to be always looking for a fight to prove that he is superior, perhaps because he is insecure about his marriage. At any rate, he finds himself without any friends because he is so suspicious of the men, suspecting that they are interested in his new wife.