B, I am so sorry to hear what he's done. I could just throttle him for what he's putting you through. I know this is very difficult, but he's really not doing this to hurt you, even though it appears to be otherwise.
It's hard to say why he would even do this, knowing that you woud see the car seat. The ow could have been putting pressure on him to make a claim and what better way to make that claim than a car seat, not less.
It's time to step away even further and let the two of them face each other off w/o an interference from you. The sooner they have all of that "fun" time, the sooner (we all hope) that the affair will end.
Please, please take care of yourself and your children. Put the focus back on you and your children.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
