If Crystal Act 28 was the first ever episode you saw, you'd think they lived together. They sure are close. I wonder if Endymion and Serenity were engaged/secretly married. They have the easy intimacy of a long-time couple. I think I heard some speculation that it was the equivalent of a summer romance that ended in an exceptionally poor way, but it looks more intense than that from Usagi and Mamoru's current relationship.