Hopefully someone will be able to read this, because I am not sure where it is going to go. I had pick up my Mom's car today and my mil offered to help. So we go to get the car and are talking along the way. She often brings up the ex. Well today was no exception. She had asked about a nieghbor of mine who is splitting with her husband and it went from that to how she feels the ex says too much to the kids about things. So my mil said that sometimes she would like to tell the sd the truth. bm had an affair and left the marriage. mil doesn't tell sd to save the kids from this.
I agreed that it would not do the kids any good to know this and added that no one should say anything negative to them about bm. I feel they have to form thier own relationship and opnions when it comes to their mom.
My question is why does she need to tell me this? Does she feel like ex made a big mistake and that her son should still be with his first wife? Or that maybe that ex ruined son's happiness? Does she mourn for how it used to be? Am I just nuts??

Thanks in advance for your input. I really appreciate you all.