I am not really sure you have to explain your position to your H. Granted, I have not read your entire thread but I feel its a safe guess that your H is clear that you would prefer to work on the marriage. So, if your H does not share that same desire AND has a OW (even if the R with the OW is falling apart) what exactly is there to explain?
I would simply say "H, my desire to work on our marriage has been well noted and while I would prefer a different outcome, the time has come for ME to make some changes so I can move forward with MY life. I will no longer tolerate you living here while you are having a R with OW, its disrespectful to me and the children. If your choice is to carry on with OW and not work on the marriage then you must move out as this is no longer a healthy environment for ME and OUR children to live in".
The "less accountability" thought process you have is troubling to me along with the idea that your sister in law will "keep tabs" on him and report back. To me that says you are not detached and you are using the separation for reasons that could really backfire on you.
You need to be able to set boundaries and detach no matter where your H lives - at the family home or in his own apartment. In fact, you will be much stronger during the duration of your separation if you can learn to do that BEFORE the physical act of separating takes place. I do agree that when a WAS isn't around all the time it does sort of propel you forward but it certainly isn't the tool you should use to detach and set boundaries.
As I said, IMO there is nothing to discuss. If he doesn't want to work on the M and he is vested in a R with OW then only you can decide if you are comfortable having your H live in the family home under those circumstances. I didn't allow it.
In my case (which worked for ME and not necessarily my M) I made the choice FOR my H. You don't want to be married, you don't want to explore what we could rebuild and you want OW then you need to leave. I helped him pack and we hugged goodbye and that was it. This was in April of 2008 and our legal separation papers will be filed tomorrow along with out divorce case being dismissed. My H is still with OW (not a good R at all, she is needy and jealous and demanding and clingy) and he has a fantasy that he and I will get to know one another again and the legal separation will "wipe our slate clean". He is welcome to have any fantasy he likes, I just won't be a part of it.
Do what is best for YOU not what is best for your H. With all due respect your H has has OW, you, the happy family home and thus far has suffered no consequences. You on the other hand have suffered them all.
