So her AP is married with small children and you're all, including YOU, letting this poor woman (his BW) live a lie like this? Has she been notified about what's going on because if there is anyone in this whole situation with even a shred of moral decency then she needs to be in the loop as to what her scumbag husband is doing with your home-wrecking wife.
You seem like a decent guy so please don't compromise your own morality in this matter or you're just like the cheaters. Perpetuating and living lies.