... I think Darcy has compelling reason to believe Lizzy is in love, or at least seriously infatuated, with Wickham. I realize we all agree that this is in his mind, but it's not clear to me that we all understand how compelling his evidence is.

Recall that their last meeting before Rosings was at the Netherfield ball, where she accosted him with Wickham's tale, to which he made no real response. Recall that at this same ball, Caroline Bingley accosted Lizzy with her interpretation of Darcy's version of his interaction with Wickham, characterizing Lizzy's attitude toward Wickham as "your favourite".

It's clear that among the Netherfield group, Lizzy and Wickham are already regarded as an item, maybe even a couple. And Darcy never sees her again until they meet at Rosings.