Hey Sherry, glad your weekend went ok. IL's are always a touchy subject, my MIL is going to be staying with me for a few weeks and I know we will talk about our R...I will probably tell her, not in detail, that he is involved in some sort of affair...she won't say anything to him but if it comes down to it I want them to know that I am not the bad guy here....not that they necessarily think that anyway.
I wouldn't tell him your plans...call him as late as possible it is respectful to let him know if you are not going to be home for dinner...do it as often as possible, if you can, leave the kids with him and go out by yourself...