Hi Hon - don't really know what to tell you - you are there, not me, but I have suspected all along that things were continuing with the OW - what man in his right mind would keep ex-OW around as an employee? Think - what worked for you before to draw H away from the OW? Whatever it was, I think you need to repeat it. I hope it was withdrawing, because I do think a LRT is in order - but you have to be ready to take that risk. Also, you may want to hold off on forcing ANY step until you have an opportunity to go snooping through the financials- I suspect you may find money hidden who knows where - maybe an attorney can help you with this. I think you need to protect yourself financially.
Now, maybe he's just a conflict-avoiding wormboy and nothing's going on. What would your approach be if you KNEW he and OW were completely through? What would your appraoch be if they were still carrying on an affair? If the approaches would be completely different - then you may need more information. I know DB says not to snoop - mostly because it gets you so worked up you can't DB properly - but this may be an occasion where hiring a P.I. could settle things once and for all as far as your doubts go.
So maybe you should stall for time until you figure out what's really going on? If it's innocent, you don't want to push him out of the house - might be pushing him right into OW's arms. If the affair is ongoing - a dose of reality therapy may be what's called for, especially since he still seems ambivalent.