Sidney sends Juliet a telegram explaining that he'll be delayed; he fell off a horse and broke his leg. He says that Piers is nursing him. Juliet then writes Sophie, imploring her to not run off to Australia to take care of Sidney. She reminds Sophie that Sidney is a horrendous patient and clearly doesn't want them there. Juliet says she's going to think about her new book idea in honor of Sidney.
Because Juliet recognizes that Sidney is perfectly happy with Piers, she does her best to take care of Sidney by respecting his wishes and making sure that others do the same. This also allows Sidney to become closer to Piers and possibly, bring Piers back into the fold of the chosen family.
Juliet turns the subject to Mark. She reprimands Sophie for asking if she's in love with Mark—she insists that Sophie needs to be more careful if she's going to snoop, and ask roundabout questions instead of direct ones. Juliet throws out facts about Mark such as his favorite author and favorite color, but says she cannot answer if she's in love with Mark. Juliet says she's getting tired of the constant nights out.
Juliet's recognition that she's not enjoying so many nights out tells her that a life with Mark isn't something she'd actually enjoy, as a number of character simply that Mark wouldn't stop taking Juliet out just because they were married. Her lack of commitment should also tell her that she's not in love with him.