Mike makes it clear he doesn't even want to be friends with Susan anymore after she finds the Valentine's Day card she made him among her possessions he's returned.
Karl, Susan's ex-husband, shows back up on her doorstep after he breaks up with Edie. Julie's away, so the two reminisce over a bottle of wine. Karl confesses Edie dumped him after discovering a photo he still kept of Susan. Moved by this admission -- and all that wine -- Susan ends up in bed with him. As Julie discovers to her horror the next morning, when she finds them in bed together. Susan tells Karl the sex was amazing, but when he says he wants to start things up again, she firmly tells him that she wants to move forward, not backward, and a reunion with him just isn't going to happen.