1. If you want to explore reconcilliation you need to start sending him a consistent message
a. Your infidelity is hurting me, hurting you, and hurting your entire family - everyone feels awkward and hurt now and it won't get any easier for anyone unless you stop b. Your infidelity is attacking another home with CHILDREN in it... THAT household's marriage - good or bad is NONE of your BUSINESS... if THEY end up divorcing that is THEIR choice and he needs to get away from that and let them sort things out if they can c. Your infidelity is hampering any chance of us repairing this marriage and providing a safe and quality home for our son. d. Pursuing this infidelity further will do a LOT MORE DAMAGE than has already been done e. You want to save your marriage f. You are hurt, but you are willing to attend a session with a GOOD FAMILY-ORIENTED therapist... NOT a shrink! A real couples counsellor who worked and is familiar with infidelity as an addiction. If he's willing to do that much for his family you are as well.
2. You need to find yourself a good couples counsellor for both of you to start seeing
3. The FIRST ORDER OF BUSINESS the FT will attend to his your H making a commitment to NO CONtACT and FULL TRANSPARENCY with you at all times.
Right now you are sending your H mixed messages. You called everyone about the affair, you haven't filed for divorce, but you also leave him assuming you want to divorce... he's going to be very confused as to what you WANT right now.. and that needs to be attacked as soon as possible. He needs to know what you want, and what you expect from him bare minimum right now.
Ignore his script talk.. its nothing to get indimidated at... he's going to blame you, him, life, everything EXCEPT his infidelity...
Don't try to compete with OW, she's beneath you... dont' dignify her or this affair trying to compete like a teenager. Just confront him to stop with the points above or tell him things are going to get a lot worse for him and his son (divorce means he divorces his son too, not just you.. many wayward spouses think they can carry out a divorce and their child will be completely isolated from that... he's deluded.. there are facts all over the web to challenge him.
You COULD hold off on the confrontation and let the FT do it but then there is a delay. You are likley best to do it yourself... with his parents there or otherwise.
4. Get some physical proof of a PA - an email or something.. hotel bill etc... to show his parents so they fully believe you... and when your Husband lies to them again after they have seen the hotel bill or email.. THEN you should get 100% support from them... people don't like being lied to... never met anyone yet that enjoyed that at all. If you can prove to them he's lying to them and have them actually WATCH him LIE to them then it will hit them hard enough.