dawgy, let me give you a little more insight into my in-laws. Not only did the anger tear up my MIL, but all of her hatred for my FIL eventually made my W somewhat bitter towards my MIL. She now has a better relationship with her dad (the one who cheated and left) than she does with her mom. I'm sure their M fell apart with equal blame up until he cheated. He (and your W) were wrong for pursuing an A while still married, but they also both feel/felt justified in their actions at SOME point. My FIL probably had many chances to place blame on MIL in front of my W, but he never did. Meanwhile, MIL harbored that hate and never missed a chance to take a jab at FIL. For the first few years, my W was probably like your S, on the LBS's side 100%. But move 10 years down the road, the pain from the A fades quite a bit in the child, yet they still see the bitterness of the LBS. It hit home with my W one night on my FIL's 60th bday. His two D's and his two sS's (along with me) surprised him for dinner (everyone was from out of town). It was a truly magical evening. At the end, FIL was hugging his D's probably for the first time in 15 years and was crying in their shoulders, expressing regret for what kind of father he had been. My W was so incredibly touched. Later she told my MIL about it and MIL just responded coldly, "He never seemed to care that much when he was here." It ruined W's night and that was the start of the decay of their R, in my opinion.
Regardless of what happens with your M, you need to really decide if that's the kind of path you want to start walking down with your S.
Me 38, WAW 30 D11 (former marriage) S2 T 8 years M 3 years BD 8/20/23 S 8/20/23