Catherine flip-flops on the idea of marriage throughout the novel. She always finds some reason not to get legally married, but she’s a true believer in acting married.
I leaned forward in the dark to kiss her, and there was a sharp stinging flash. […]
"I’m so sorry," she said. I felt I had a certain advantage. (5.52)
This is the only time we see Catherine act violently, and she doesn’t like what she’s done. She does want Frederic to kiss her, as we see. We wonder if she slaps him because she doesn’t want to be thought of as being too "easy." He seems to take her slap as an indication of just how much she does want him.
"I don’t want anyone else to touch you. I’m silly. I get furious when they touch you. (16.28)
Throughout the novel, Catherine expresses her jealousy in funny ways. At another point she says she wishes she’d been with the women Frederic has been with so she can talk about them with him.
"But watch out you don’t get her in trouble. You get her in trouble and I’ll kill you." (17.25)
Helen Ferguson thinks of being pregnant as being in trouble. She sounds like what we might expect a father or a brother to sound like. Later, when Frederic comes to Stresa after leaving the retreat, she sounds more like what we expect a mother to sound like when she cries about Frederic and Catherine not being married.
"Don’t talk as though you had to make an honest woman out of me. I’m a very honest woman" (18.39)
Once again Catherine suggests that marriage as an institution is an empty shell, that it can’t turn her into something she isn’t already.
"What’s the matter, darling?"
"I never felt like a whore before." (23.143)
This is probably the first time Catherine and Frederic have sex together outside of his hospital bed. Part of why she feels like a whore is because she knows that not just any hotel would let them get a room for a few hours, married or not. When they have sex in the hospital it seems like part of her nursing duties in a way, and therefore acceptable.
"We’re happy," Catherine said. "You’re a sweet Fergy." (34.58)
What’s the deal with Catherine and Fergy? Fergy loves her lots, in her old-fashioned way, wanting her to get married and everything. But does Catherine love Fergy? She is last mentioned, by Catherine, when she and Frederic are fleeing to Switzerland. But, since Frederic is the narrator, it’s hard to judge the two women’s relationship. This is Frederic’s memory and he might not even know if Catherine gets in touch with Helen. He sure won’t know if Catherine thinks about Helen. And even she tells him, he might not remember.
"Nonsense. Rowing in moderation is very good for the pregnant lady." (37.53)
We think it’s pretty brave and strong of Catherine to get in to a boat in the middle of the night, pregnant, not even complain, and even offer to help row.
Book 5, Chapter 38
"No, let it grow a little longer and I could cut mine and we’d be just alike only one of us blond and one of us dark." (38.143)
Catherine wants to literally "cut" through the outward appearance of gender difference.