Marriage is a two sided deal where one supports the other, when that other is at his weak point.
Cersei likes to think about herself as a strong one (and somehow at the same time a helpless victim), but she has never really tried to rein Robert in and make him love her or respect her or be a better man in any way. She actually enjoyed ruining him. Happy to have a cause to complain and cling to her illusions of being someone who "never had a chance".
A man is responsible for himself, however Robert was easy to indulge and could have been steered by some strong presence. Khal Drogo was changed by Dany and he was a lot less likely to bend.
Cersei banked on Robert and then abandoned him. She made her own bed, but did not want to sleep in it. With Robert. So she broke all the rules there was. And made a bad husband into a crappy one and a bored king into an angry one.
Bad wife and a bad queen. And yet Robert is blamed








