I think. He is needed to communicate the information about Darcy to Lizzy ( that Darcy separated Bingley and Jane). And he is there to show how attractive Lizzy is to men.

I think that Lizzy's manner is so open and different from other women of the time that she gets misunderstood easily. Men think she is more interested in them than she is. She doesn't seem to realize that herself, or if she does, she is quite a flirt! I would think there is a little bit both. She is a (very) young woman and enjoys the company and admiration of men. Maybe there hasn't been that so much before in their little social circle?