"Itís that if people who know him well and have seen him in love before, observe his behavior and come to the conclusions they do. Then itís likely his behavior leads people to these conclusions"
Darcy notes that he's seen Bingley in love before, but he does not think until Sir William gives him a hint that Bingley's attentions are leading people to think that Bingley is goigng to propose to Jane.
I would say that Wickham HAS spent as much time with Eliz and shown her a lot of attention, then he's off to pay court to Miss King.. and Liz, while she's a little piqued, she isn't breaking her heart or refusing to look at other suitors. While Jane may feel Bingley's leaving a bit more deeply, I'd say that she's too sensible to break her heart over him. If she refused another suitor, it would be because she wasn't yet over him, not because after he left for London, she was clinging to a hope that he woudl come back.
I think that Darcy was cautious about Eliz because he was so unsure of his feelings, and because he must have realised that he was sending out mixed signals, half acting as if he were intersted in her and half the time ignoring her. Col F is spending a fair bit of time with Eliz, but he KNOWS that he is not enough in love with her to marry her without any money so he gives her a polite hint. But BIngley is not as sure of his feelings or lack of them as Col F is.
I know that courtship was a delicate and difficult affair at the time, relying on hints and signs but still I dotn think that a man had to worry all the time that a girl was going to braek her heart for him, or have her parents chase after him with a shotgun, because he had been a bit attentive, and then moved on. Fred Wentwroth is in a somewhat similar situation with Louisa, that he has been paying her attentions, he realises a bit late that other people are expecting them to get engaged. And he doesn't quite know what to do. SO he feels that IF Lou is likely to be heartbroken, he will ask her to marry him, but if he can weaken her attachment by going away for a little, he'll try to do that..