In the original series, Susan Sharon first appears in Season 2, Episode 2, “The Awful Truth.” In the episode, her husband, Richard, kicks Carrie out of their apartment after she and Susan go on a night out.
Afterward, Susan calls Carrie up to get her advice on whether she should leave her husband. Although Carrie tries to sidestep the conversation, Susan takes their talk as a sign to leave Richard. But at the end of the episode, Susan and Richard reunite.
Source: https://www.distractify.com/p/susan-sharon-and-just-like-that