After Amanda and Elyot make up during the "triple Sollocks," what happens that brings their happy mood down again and why?

The telephone rings. They are both initially fearful that it is Victor or Sybil calling them, but the caller, as it turns out, has the wrong number. Even though it is a false alarm, it rattles Amanda and she says that she believes love is only a fleeting joke. The phone call is a reminder that their spouses will find them and her guilt rises at the thought of the hurt she and Elyot have caused them.