The divorce cost Billy at least $8 billion. When it was announced after it was revealed that Bill was on THE plane, I thought it was probably that--the reason they got divorced. But, there was always some doubt, maybe it was coincidence, maybe it was just the straw on the camel's back, and it's more that Bill is generally a shitty person, just like every other billionaire. The more that comes out, the more it's obvious this was more than a single straw. She didn't know how far he went, she was blind-sided. I can only imagine what that argument and following negotiation was like, and what she knows, that she signed an NDA to never reveal in exchange for the money.
In the end, all billionaires are bad, even Melinda. She took the payout to shut up. She's "using it for good", but that's as much bullshit as it was when she was with Bill.
