Even if the EA was there before BD they will see it as a non factor in their decision to separate. Its not be that they lie about this in all cases, but that they have convinced themselves this is the truth because the truth is too much for them to face.

Deep down they might realize the real reason. I just think for them its easier to ignore the truth that makes them out to be the bad guy. Especially if what there doing is chasing another person to make them happy.

Sometimes I think that's why my W pursues this guy so intensely and throws herself at him. If he doesn't work out she has to face the reality she was wrong about him and everything she gave up was wrong also. She clinging to a reality that's collapsing and she might know it but cant admit it to herself. So her stubbornness keeps pushing her forward trying to force that reality to happen no matter the cost.

Accept what is, let go of what was, and have faith in what will be