It was plain to them all that Colonel Fitzwilliam came because he had pleasure in their society, a persuasion which of course recommended him still more; and Elizabeth was reminded by her own satisfaction in being with him, as well as by his evident admiration for her, of her former favourite George Wickham; and though, in comparing them, she saw there was less captivating softness in Colonel Fitzwilliam's manners, she believed he might have the best informed mind. (Chapter 32)

F is indeed a promising letter by all accounts and Lizzy likes an open manner and entertaining conservation in which the Colonel is most obliging. Col Fitzwilliam reminds Lizzy of Wickham and actually finds he has a better informed mind than her former favorite. Wickham showed up Darcy in Hertfordshire and in Kent his cousin outshines him at every turn. In Chapter 30 Darcy and the Colonel visit the ladies at Hunsford parsonage and Col Fitzwilliam immediately displays qualities she admired in Wickham—opened mannered and tempered, attentive and gentlemanlike in his behavior.

Colonel Fitzwilliam seemed really glad to see them; anything was a welcome relief to him at Rosings; and Mrs. Collins's pretty friend had moreover caught his fancy very much. He now seated himself by her, and talked so agreeably of Kent and Hertfordshire, of travelling and staying at home, of new books and music, that Elizabeth had never been half so well entertained in that room before; and they conversed with so much spirit and flow, as to draw the attention of Lady Catherine herself, as well as of Mr. Darcy. His eyes had been soon and repeatedly turned towards them with a look of curiosity; and that her ladyship, after a while, shared the feeling, was more openly acknowledged, for she did not scruple to call out -- (Chapter 31)

Col Fitzwilliam fancy’s Lizzy and she also likes him but in Chapter 33 he warns her he cannot marry where he chooses. IMO he does this because he has been too apparent in his admiration of Lizzy and she might think his intentions are serious. This is much more civilized than Darcy’s “ignore the lady for a day approach” in Chapter 12. Is there any chance that Lizzy’s manners have given Col Fitzwilliam the idea that she expects anything? Lizzy’s manners do mislead Darcy during her stay at Netherfield; he believes she knows he is attracted to her and believes she would have him if she could. Lizzy’s manners do not always portray what she intends:

Elizabeth, having rather expected to affront him, was amazed at his gallantry; but there was a mixture of sweetness and archness in her manner which made it difficult for her to affront anybody, and Darcy had never been so bewitched by any woman as he was by her. He really believed that, were it not for the inferiority of her connexions, he should be in some danger. (Chapter 10)