Alcee Arobin is introduced as a character. Why? How does he contribute to the story?

In my opinion, Alcee's character and previous relationship or interlude with Edna reveals that she has "wandered" before. Robert and Edna have only carried on a flirtation up until this point, something which Madame Ratignolle advises Robert to nip in the bud, as nothing good can come from it.