Well, by now we know Alex did go away that day and came back some time later. I think he overheard her being so upset about being blind and all and was struck by how much she apparently cared about "Frank". As to why he left instead of staying and consoling her, my best guess is that he took some time to digest the news and compose himself before going to her and being her best friend. I mean, he is a man in love, he wants her for himself. As caring and considerate and kind as he can be, he is merely human, and was very much hurt by Emma's declaration of love for someone else. Besides, I'm pretty sure he didn't know of Frank and Jane's relationship becoming public, so he may have gone to Ryan or Annie to ask about it. Once he made sure that was the problem, he could have gone to Emma.
In the novel, when Mr. Knightley hears of Frank and Jane's engagement, he is in London. True, he rushes back to comfort Emma, but by the time he arrives in Hartfield he has come to terms with the news. In EA, Alex hears Emma talking about her love for another, which Mr. Knightley never did. Yes, George Knightley thought Emma was in love with Frank, but there's a great difference between a supposition and a certainty. Is it any wonder that Alex left when confronted with evidence that Emma's affections were -supposedly- Frank's?
Also, there is the matter of Mr. Knightley being envious of Frank Churchill. In the novel, his admission of envy makes him human: he is a good man, has many qualities, but is not above feeling envy for another. In EA, there's no mention of it. Alex's humanity is shown when he leaves after overhearing Emma: he is shocked and doesn't feel up to being the consoling friend when he himself -in that very moment- needs consoling.
In the novel, when Mr. Knightley hears of Frank and Jane's engagement, he is in London. True, he rushes back to comfort Emma, but by the time he arrives in Hartfield he has come to terms with the news. In EA, Alex hears Emma talking about her love for another, which Mr. Knightley never did. Yes, George Knightley thought Emma was in love with Frank, but there's a great difference between a supposition and a certainty. Is it any wonder that Alex left when confronted with evidence that Emma's affections were -supposedly- Frank's?
Also, there is the matter of Mr. Knightley being envious of Frank Churchill. In the novel, his admission of envy makes him human: he is a good man, has many qualities, but is not above feeling envy for another. In EA, there's no mention of it. Alex's humanity is shown when he leaves after overhearing Emma: he is shocked and doesn't feel up to being the consoling friend when he himself -in that very moment- needs consoling.