I have my opinion and this is what I think happened. Over the years I have read numerous articles about both of them, before and after the marriage. Maria saw him playing those roles in
several of his movies and decided she wanted to get to know him. He was a physical hunk, the kind an Alpha female would go for.
Arnold had grown up with European values that is somewhat different than values here in the states. An occasional affair for a married man is overlooked, and often expected. Arnold had women
throwing themselves at him from the time he was a young man. Having affairs with all these women was so ingrained in his physique that when he got married there was no way he was going to stop.
Even if he had wanted to, it was too ingrained into him, too much a part of him. It's who he was.
So after the marriage, he may have slowed down, but he never quite. There was bits and snippets about his behavior during filming coming out occasionally, but no one was paying attention. When the
maid got pregnant, he knew he needed to keep it quite. So he kept it quite for years, and could have continued for many more years if he had wanted to. I believe the marriage was over between
them, but neither one wanted to be the first to initiate action. Arnold got tired of waiting, so he let it slip about his having a son by the maid. Maria looking for an excuse, jumped on it and filed.
Arnold will now be free to go and do as he pleases again, and nobody will care, just like before. Women will still throw themselves at him, and he will continue to do what they want him to do.