I noticed that too, maybe Chopin is trying to say something about Edna's desires? It also says a lot about the narrative style.

that it does have to do with the narrative style, the tone he wants to bring upon the reading

I'm not sure, but i wondered about it as well! Maybe she was saying that you cannot have two lovers without some sort of pain. (the woman..

in black representing pain or sorrow) she always is nearby to balance out the joy between the lovers

I think that it was foreshadowing... death would follow Edna in her lovers escapades

In this time period it's customary for widows to wear all black - so we're seeing the beginning and the end of the relationship spectrum.

There's definitely foreshadowing going on with that, too.