This list was made in response to this request for stories where Jack and Ianto break up (not necessarily permanently). These stories are tagged on Delicious under storyfinder:jackiantobreakup. Although all these stories feature Jack/Ianto (one way or another), several of them also have Jack or Ianto paired with others, noted after the links.
( Jack/Ianto Break-Up Stories )
( Jack/Ianto Break-Up Stories )