Faulk I have been thinking about your ds this weekend and I think you should talk to him about what's happening. It sounds like he is a sensitive boy and the whole situation could be having an adverse affect on him. The fact that no-one is talking about it will be hard for him to reconcile.
I think you should ask if he has noticed that dad has been a bit irritable lately, or mum has been a bit tearful (or whatever you think he may have noticed).
Explain to him that you and dp have got some big decisions to make and at the moment you can't agree on them. Tell him that it is nothing that he has said/done or not said/done and that you both love him as much as ever.
If he asks if you are going to separate, be honest. Tell him that it might happen because if two people cannot be happy together, then separating is the right thing to do. But, at the moment, you are hoping that you will be able to sort things out.
If he asks, is it her (OW), tell him it is partly to do with that but mostly because you and dad haven't been able to work as a team and support each other and teamwork is very important in a family.
He will probably ask what will happen to him because that is what most children are concerned about. Tell him he will still have his mum and dad and they both love him. He will have a home and his friends, and go to the same school (if indeed you think that will be possible).
Tell him that if he has any worries or wants to ask more questions, he can come to you anytime.
I think this will help him feel more settled. He might be finding it hard to concentrate at school or be worried about an uncertain future. I also think this will help you because if you do decide to separate, the worst part of telling the children will be pretty much dealt with.
Normally I wouldn't suggest involving the children or telling them about marital dischord Faulk, but in your case I do think that your ds is reacting to the circumstances and it's better to talk about it than leave him anxious and worried.
What do you think?
Hope you're ok btw x