Basically I found out after leaving my ex that he had been cheating on me for half our marriage with his ex fiance who was also married at the time with 2 dc (very similar age to mine). This was almost 1 year ago I found out about it but ex and ow tried to cover it up. It was a combination of me and ex mil putting the 2 and 2 together that we worked out that although I had taken the initiative to leave he had already been in a relationship with ow for a number of years so wasn't really invested or concerned about the marriage ending.
Anyway at the time I was obviously in shock to put it mildly. I had left because he was narcissistic and controlling. But to find out that he had also been lying and cheating for the majority of the relationship was distressing. What made it more difficult was that my dcs were spending every other weekend with the 2 of them acting like a happy family glossing over the sordid origins of their relationship. Oh and ex was still angry that I had left and was trying to control me despite being separated which culminated in a domestic violence incident which eventually lead to me going no contact.
Anyway at the time my eldest dc (5 at the time) outright asked me why I didn't like them. I had never said anything to him but obviously something from my response or mannerisms must have indicated that to him. I gave what I thought was the simplest answer at the time which was that their dad and her had done something bad to me but it had nothing to do with him and he was loved by both parents so should just enjoy his time with either of us. My son kept repeatedly asking me what had they done to which I responded that I would tell him when he was a grown up.
I have regretted it since then because my son keeps periodically asking me when I will tell him what they did. He is 6. Anyway after asking me again recently about it I told him look it doesn't really matter anymore, it doesn't affect me and it's not important go and have fun and forget about it. However unknown to me ds went and asked ow about it who said to him she had done nothing wrong to me and in fact it was me who had gone on her Facebook whilst she had not gone on mine.
I was livid when my son told me and said well she didn't need to look me up because she knew about me for the whole time I was married to your dad but I knew nothing about her. I only found out of her existence because my older ds told me about her. Their dad had declined to tell me he was taking them to stay over at her house. Anyway I'm sure he will go back and relay the news to which they will respond with some other lie or half truth. I was wondering whether I should just explain to my ds in an age appropriate way what happened so he stops worrying about it and going back and forth between us trying to find out the story.