[There's a long pause full of hesitation as Constance reminds herself that Arthur cares about Anne, would never do anything at all to harm her or cause her distress... if there's anyone she can trust about her, it's Arthur.]
... You can keep a secret, right? [She still has to check. And even so, what she's thinking of telling Arthur is hardly anything but a small part of exactly what she suspects--she would never betray Anne like that.]
I believe she might be looking forward to meeting someone.