Your Mother broke up with your Father for another man, which your father already known about, so he didn’t have much of a shock, and surprisingly he’s been happier after she left him, he is now able to give you more attention and affection then he used to be able to give, another reason he is happier is because your mother didn’t take you with her and left you with your father, which made him happy. You’ve also been happier she left, she wasn’t the best anyway.