I've NC'd for this because it could be outing - I'm also a dad, rather than a mum, if that makes any difference.
I have two DSis, one older and one younger. DM doesn't have any contact with me or DSis2 (well, she attempts to contact us and we don't respond - that's a whole new thread), but is in very regular (but not pleasant) contact with DSis1. When I was a child, DM had an affair with DSDad and left my DDad. We moved into a house with DSDad but a few months later, he broke up with DM and we moved into a rented house. Then, my Godfather, my DM's ex from before DDad moved in (almost immediately - within about a week or two). After about 6 months of that, DSDad wanted DM back so DM left my godfather and moved back in with DSDad, married him. I didn't see my godfather at all during their marriage.
Around 10 years ago, DM and DSDad broke up (initiated by DM having another affair). By that time, Godfather had married someone else and moved away. DM bought a house and began a relationship with another man, who turned out to be married - that relationship has now ended. DSDad has said to me that there were numerous occasions during his marriage to DM when godfather would contact her inappropriately - even after he got married. Since I went non-contact with DM, I've had numerous messages and phone calls from Godfather saying how hurt she is by it and that I need to get back in contact with her. From what he's said to me, he's very well-informed on her version of events so they've obviously done a lot of talking - when a relative of mine died recently, he found out before I did and messaged me his condolences. Some of the messages he sends to me are in the early hours of the morning so I get the impression they're up late messaging each other. So, clearly DM and Godfather talk a lot - and this has been going on for a few years now (at least). DSis1 has now mentioned that DM is planning to move to the small town where Godfather lives (hundreds of miles from where DM currently lives, and DM has no other connection to this town). She's put her house up for sale and accepted an offer - I don't know whether she's had an offer accepted on a new house though.
Given DM's track record with infidelity and married men, and their past relationship history, I feel as though my Godfather's wife should know what's going on (if anything is, in fact, going on). But, I don't want to personally get involved (but, then again, who else will?) - but maybe that view is selfish? I know Godfather's wife is a SAHM so that's playing on my mind too because I know she's not financially independent.
I'm really looking for perspectives, largely a woman's perspective, on whether they'd want to know or not at this stage.