Advice on what to tell 9 year old about OW

[Gottanovelinme3]

Advice desperately needed!
A month ago i discovered that my husband of 12 years has been having an affair. The circumstances under which i found out meant that our 2 children and some friends and relatives were present at the time. It was awful.
What my stbxh chose to do in the immediate aftermath (before he had even spoken with me), was take our eldest child aside and tell him that daddy had been having a relationship with OW and we would be divorcing.
To complicate things further, this woman (and her kids) are known to our children. The day after, our eldest asked me several questions about OW, whether she and daddy would get married etc. I remained neutral. He hasn't asked anything about her since.
Since this all happened, stbxh has moved in with ow and her children. Our children do not know this as he continues to see them at our home or takes them to his parents'.
I have read a lot about importance of giving the kids time to grieve the end of mum and dad's relationship, not bringing in OW for up to a year etc etc.
However my concern is that our eldest is aware of OW, knows her but has not mentioned her for 4 weeks. What do i say if the children ask me where daddy is living? Do i ask eldest about whether he has any worries or questions about OW or wait for him to discuss her with me? I don't want to bring her up if he isn't thinking about her. What if he were to ask to see her? Then i'd need to tell youngest too. If relationship with OW lasts a year and the kids are introduced to her next year will they resent me for not having told them that was where daddy was living all along? It's my relationship with them that i need to protect.
I feel stbxh would go along with what i suggest as best ways to handle this, as he is acting like a clueless child through much of this...

How old are the children?

9 and 6 x

I think I would leave it if he seems to be acting normally, happy, doing okay at school etc. If he is showing signs of stress then I would just question him gently about how he is feeling about Mummy and Daddy splitting up. Don't mention OW specifically unless he does.
I do know two little girls whose Dad did precisely this to them at the same ages. It is the oldest one that has suffered the most, she is struggling 5 years later. It is difficult for children to believe they are of any importance when their father can just" choose another family, " which is how they see it. Good Luck OP

I know this contradicts the previous advice but I would talk to your 9 year old about it directly. Maybe during an activity rather than sitting and talking directly. My experience working with kids always makes me advise to talk about these things as, similarly to adults, he won’t have just stopped thinking about it, he may be creating different scenarios in his head that aren’t true or he may be worried that he can’t talk to you about it in case he upsets you. He needs to know that he can talk to you about it and what the actual situation is otherwise he might be thinking all sorts about you and his dad getting back together etc. I think if you don’t mention the OW then he will think he can’t in the future and it’d potentially effect his relationship with you in the future if he starts spending time with her.
With your 6 year old you can tell him a more simple version of it.

I really dont think that pretending the OW doesnt exist for year will work in your circumstances. If they know the other children they might tell them either now or in the future. Then your kids are dealing with abandonment and feeling they csht trust you.

Is there a counsellor at their school you could access? Some have one visiting weekly and would support in situations like this