quotes that are said ABOUT curley that link to loneliness

You really need to interpret a little here. Characterization isn't always obviously stated. Take aloof again at Candy's comment,

"Curley's like a lot of little guys. He hates big guys. He's alla time picking scraps with big guys. Kind of like he's mad at 'em because he ain't a big guy."

Curley's lack of self-esteem isolates him from any positive relationships.