Poor, sweet Charley doesn't just have a crush on Eustacia; he practically worships the girl. We pretty much only see Charley in scenes with Eustacia, and the way Charley acts around her helps to emphasize how Eustacia really is like a queen, especially on the heath.
"Here are the things," he whispered, placing them upon the threshold. "And now, Miss Eustacia –"
"The payment. It is quite ready. I am as good as my word."She leant against the door-post, and gave him her hand. Charley took it in both his own with a tenderness beyond description, unless it was like that of a child holding a captured sparrow. (2.4.63-65)
But Charley is more than just a guy with a somewhat pathetic crush. He actually turns out to be pretty heroic, and his devotion to Eustacia really helps her out. Charley is the only one who really takes care of her after she leaves Clym, and he even stops her from committing suicide.
"O, why did you, Charley? What makes death painful except the thought of others' grief? – and that is absent in my case, for not a sigh would follow me!"
"Ah, it is trouble that has done this! I wish in my very soul that he who brought it about might die and rot, even if 'tis transportation to say it!"
"Charley, no more of that. What do you mean to do about this you have seen?"
"Keep it close as night, if you promise not to think of it again." (5.4.58-61)
In the end, Charley is one of the few genuinely heroic people in the book. After Eustacia's death, Charley is nearly as distraught as Clym, and it's obvious that Eustacia had a huge impact on Charley's life. Through Charley, we get another view of Eustacia's character and what she could mean to other people.