Iirc at the time there was still "at fault divorce", and the divorce settlement was influenced by who was at fault. So a (likely overly charitable reading) of the entire thing is that Feynman agreed to be portrayed in a bad light to achieve a fairer Deal for his soon to be ex wife.
Maybe it was required to get a divorce at all but otherwise it seems that he could have settled on something “fair” without needing to force himself into it.