Red...girl, our men are sounding somewhat similar. WHAT is WITH the COCKINESS? Mine actually said to me "yeah, I'm a likable nice guy" and I'm here thinking...UM...yeah, to everyone BUT me...fakeass.
I have the same issue with the "wanting to be loved" by my WAH. I really don't know why I would even want that anymore...but I do and it frustrates me to no end.
YOU have to, for yourself, avoid playing games with him. Don't do anything to see what he'll do (*cough* advice to self). He's not human, remember? Nothing he does is going to be predictable, and the more games you play the more exhausting you will be. I'm sure he's calculating his moves, and saying whatever comes to his mind without considering the consequences. Every time he speaks about OW and everything else in terms of your R out loud to you, he is convincing himself of xyz. I noticed my WAH does this too. They don't even SOUND like the same person. Let him. Let him drown in his crazy...let him reap what he sows.
Don't worry about the inlaws. Don't worry about what anyone else is doing right now...the more you do, the more energy you take away from yourself. By letting OW and their son stay there, they're not doing anything to you. I know it's going to hurt, but even if they don't agree with their son they're likely going to support him even if what he's doing is 50 shades of messed up.