Faithful/Unfaithful

Downton Abbey Fanfiction
Lady Mary believes Matthew has been unfaithful, yet he's denying it at all costs. What's the truth?
(Changes to facts from the show: Matthew did not die after the birth of George. Anna and Mr Bates had a daughter called Beatrix, a few months younger than George. Sybil did not die during childbirth but she lost her daughter - who was subsequently called Sybil (Sybbie) - a year before George's birth. Everyone knows Marigold is Edith's daughter and she is married to Burtie. Ages of the children: George is a almost a year old and Beatrix, three months younger. Marigold is two. Sybbie would have been around two, Sybil and Tom still grieving for their lost daughter yet just about managing closure)