Jane Austen uses the relationships between Elizabeth/Darcy and Jane/Bingley to show the reader two different types of emotional love.
Jane and Bingley's romance, on both sides, was love at first sight. Bingley believed Jane to be the "most beautiful creature [he] ever beheld" and Jane found him to be handsome, gentlemanly, friendly, and easy going. After meeting him, Jane raved to Elizabeth about how he is "just what a young man ought to be." Both were equally attracted to each other, but sadly, the reason why the match broke up was that Jane was too reserved to really express her emotion. She never showed Bingley how much she cared, so Bingley was easily persuaded that she did not care.
Austen uses Elizabeth and Darcy's relationship to show the other kind of emotional love. Not all emotional love is felt the instant you meet. Sometimes the strongest love can enter as meekly as a lamb. Also, there is often a very fine line between love and hate. Elizabeth first felt upon meeting Darcy that he was detestable. However, it did not take long for him to convince her that the opposite is true.
The two romances show two opposing sides of emotional romantic love, the kind that begins with a bang and the kind that begins very quietly.