Just a summer fling?

We all know the story of Grease, a boy and girl meet over summer and fall in love, however, summer must come to an end and they go back to their respective homes, never thinking they would see each other again, but Sandy and Danny are in luck. Shortly after they restart school, they find they both attend Rydell and are happily reunited and despite their ups and downs, live happily ever after. This might sound familiar to how Robert and Edna met, but maybe Robert doesn't want a classic Grease ending for his affair with Edna.

In the book, we see that after moving to Mexico, he keeps closely in touch with some, but oddly enough, his letters seem to be focused on Edna. Now, why wouldn't he just send her a letter and ask the questions he has personally? My theory is that he thinks of Edna as nothing more than a summer fling, rather than a potential lasting relationship, as Edna sees it. We see that he is curious about her when he writes his letters, "“Yes, to me. Why not? Don’t stir all the warmth out of your coffee; drink it. Though the letter might as well have been sent to you; it was nothing but Mrs. Pontellier from beginning to end.”" (68). Obviously he wants to know about her, but isn't asking her specifically for a reason. Unfortunately, I do not see a happy ending for their relationship, maybe Sandy and Danny should teach them how it's done.