This might be long so apologies in advance. NC.
One of my best friends has been married for 15+ years to a DH I have always got on well with. We socialise together as couples a lot and have been away together etc.
In a nutshell, the history of their relationship is that he cheated on her with two different women about 10 years ago, two young kids at the time and they patched it up. She has had suspicions about a few other women in the years since but he has dismissed it as her paranoia because of what has happened before. To be honest, I suspect that's true. I don't think he cheated again. But their relationship is not in great shape now, they haven't had a sexual relationship in about 5 years and she is incredibly possessive of him. Somewhat understandable given what happened but none of it that great ultimately.
They work for the same business but in different departments. Within the last couple of years, a new woman, significantly younger than both my friend and her DH, started working there and my friend took an immediate dislike to her. She flirts with the DH (she is married herself but sketchy how solid it is apparently). She also contacts him out of working hours. They have had a lot of rows about this woman. My friend has discovered that the woman is not well liked in the office for her behaviour towards lots of men but particularly the DH. There have been rumours about them circulating at least since last year. My friend only recently became aware of this and has not told her DH that she knows (overheard a conversation between other colleagues about it).
My friend has also noticed that the DH and this woman stopped being friends on social media quite abruptly in the last month and then became friends again in the last couple of weeks. She also apparently told someone in the office that she had "contact" with a married man who had then stopped all contact but she didn't clarify further.
My friend is now convinced something has happened with this woman but doesn't know how to confront it if she even has enough to confront.
Any advice on how to advise my friend? I don't want to make her even more paranoid about this if, objectively, there doesn't seem to be much to it.