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Thanks everyone for the input. Just to answer a couple of points raised. I think I'm in a better position to manage the kids, if my wife was to move out I don't think she'd manage on her own very well, not due to incompetence just general stuff and loneliness. She's pretty well looked after at the moment and isn't very proactive. I wouldn't want to put her in that position and I'd be very comfortable in isolation if it came to me moving away.
She's also in a state of denial or indifference, I can't decide which one it is. One of the main issues we have is the non-physical intimacy, we don't talk to each other about anything, even after counselling where we had loads of tasks and ideas to get us talking just fell flat. I think one of the reasons things have gone on like this for so long is that I thought it was just me that wanted out, but now it seems like it's very mutual even though she maintains that splitting up is not what she wants. I'm sure there's an element of what people, and especially her family, would say. When I mentioned separating previously the first question from her was what would happen with the house so I think downsizing is a bigger concern.
Waiting for GCSEs has been my plan for a number of years, it seems like as it gets closer it's becoming more difficult though, like when Christmas suddenly becomes exciting when you see Santa hats in Tesco (unless it's August of course when that just drives you nuts!!!)