I know your above post was venting but it sounds like you need to slow down a little.
Your H is in another R with OW is that a deal breaker for you? If he is actively involved with this woman then I think you should sit down with him and discuss the parameters of your relationship with him.
This might be done best with a C present. I told my H in front of a C that I did not want him introducing our girls to any OW until he was getting remarried. Having the C there help create a boundary and prevented an argument. It also allowed me to use her to ask him the some questions so I was the judge, jury and the executioner.
My thoughts about drawing the line with him does not mean I think that their is no hope for reconciliation. I just think he needs to have a clearer understanding of what leaving the family means. It is not leaving you and bringing the kids into a new home. I think a good C will explain that better then you can.
I would ignore his "underhandedness" right now and try to focus on the questions that you can answer. Is his relationship a deal breaker?
---- M 39 H 35 D5,D4 M 4 T 9 ILYBNILWY 5/18/11 Left 7/11/11 Divorced 12/1/13