I'm not really thinking deep here, just spitting out my first thought when I read your question.
It seems like if the tables were reversed, and he was moving in with OW, you would have no choice to see it as significant, right. So, when he's moving in with you, no matter what the reason, she would have to see that as SOMETHING, and it IS something in the grand scheme of things.
I do agree with OT though, and you should not do anything that compromises your boundaries for the sake of experiment. IF he moves back in, it should be because YOU want it and you can deal with the situation as it will be. Maybe, as I think you have suggested in the past, you and he can try to more accurately define what the situation WILL be and conditions in which you will terminate the situation. I think OT mentioned that she thinks he may not be ready or willing to commit to a totally closed relationship yet so if he can't do that, then you have a decision to make. I think you know I don't really agree that having him out of the house, whatever the sitch is, is absolutely the best thing. I think, like many others, you CAN have him in the house with something less than a full commitment but you have to be able to accept, and more than that, want that.
Maybe I am WAY off base with this but it does seem like your decision is not made and there ARE things to consider. In the end, I think you have been remarkably strong and centered through all this and getting more-so by the day. You WILL make the right choice and of that I have no doubt.
