Difficult dynamic. Bear with me.

I (29F) was in a relationship with (fake names) Tom (39M) and Kathy (35F) for 8 months, 1 1/2- two years ago. Tom and Kathy have been married for a while under 10 years though. Our relationship ended very poorly and we are all no longer friends. I am now dating Phil (36M) and have been for a year. We all have known each other for a few years.

I found out that Kathy sent nudes to Phil (which he ignored) two years ago, around when we all met Phil. He had ignored her attempts and moved on from it. He had mentioned to me before she had made a few off color “in another life” comments but he had brushed them off. He ignored the nudes and didn’t think to bring them up until Kathy came up in conversation recently. Kathy and Tom were on good terms at the time, actively trying to get pregnant (they now have a baby, conceived around that time so that makes this much more complicated.) Not having any problems that I was aware of, and I was very deeply invested into their relationship.

I feel like I should tell Tom that Kathy emotionally cheated on us and went as far as sending nudes. But I also know Kathy is a manipulative, vindictive person and could turn this around on me, even with proof (Phil still has the nudes and the metadata shows when they were taken). I am fighting between the morality of doing the “right” thing and just letting it go. Kathy also had pursued me for years prior to her formally bringing it up to her husband so this is not the first time she has crossed the line that I’m aware of. I do think she would do this again, given the chance. Tom doesn’t deserve this. But I don’t think he’d be receptive to it.

WIBTA if I told Tom about Kathy, potentially breaking up their family? I feel like he has the right to know and can make his own decision from there.

ETA: I know that I would want to know, but that doesn’t mean that I should tell him. I’m unsure if it’s my emotions of feeling cheated on are clouding my judgement. I am leaning towards not saying anything, for the record.