I am so sorry you are back to this place again, May.
However, there are a few things that stand out to me, some of which have been mentioned by previous posters. Firstly, although it feels like you are back in the same place you were in January, I am not sure that your H is in the same place as he was then. OW has done you a service by forcing his hand to a certain degree. Although you can't control her, or him, it is clear that she is putting him in a place of an ultimatum. And you have been clear about your boundaries surrounding him leaving the house. So it's on him and you can't be blamed for the fallout of his decision, either way.
What other boundaries could you put up and still maintain the hard work you have put into the R for the past five months? What do you need to survive this right now? I agree with everyone else that you absolutely should not be his BFF or sounding board for the purpose of sorting through his emotional quagmire. And asking you for 6 months is absolutely ridiculous, but illuminates the fact that he is indeed in a between a rock and a hard spot and only he can save himself (though he wants you to).
Step out of his way as much as you possibly can. This is on him, it is not your fault and you can't save him.
