I've heard that he made a list of elaborate rules for his first wife to follow, including that she should cook for him, cease speaking when told, and to not expect affection. Also that his second wife was fully aware of his philandering, even to the point where he would write letters to her describing his relations with other women.
Are these stories true? Do they paint an accurate image of Einstein as taking a (for lack of a better word) selfish role in his marriages?
What was the effect of this treatment on his second wife? Did she accept it?
I'm currently reading Einstein by Walter Isaacson (I'm past the point where Einstein's second wife dies). Since there aren't any experts here yet I'll get the ball rolling by attempting to sum up his take on Einstein's marriages.
His first wife was Mileva Maric who was also a student at what would become Swiss Federal Polytechnic in Zurich. She was not the greatest student (but neither was Einstein, due to conflicts with his professors) and never managed to pass the exit exam to get her diploma.
According to Isaacson, their romance and marriage was happy, 'true love' at first, although it was opposed by Einstein's parents because Maric was plain and walked with a limp. Einstein and Maric had a daughter out of wedlock who most likely went to live with Maric's family and then was forgotten by history.
Despite his family's protests Einstein married Maric and after some struggles found his famous first job at the Swiss patent office. They were happy at first and they had two sons. They described their lifestyle as 'bohemian.' Einstein had his miracle year in 1905.
At some point around 1910 after the birth of their two sons their marriage went sour. Einstein was a workaholic who probably spent less time with his family then is considered normal, preferring science to socializing. Isaacson makes Maric sound somewhat unstable and needy. Einstein wanted a divorce but Maric was somewhat pathetic and inconsolable (manipulative?) so Einstein (under pressure from family friends) agreed not to divorce her but instead gave her the ultimatum you described above as a condition for continued marriage.
Meanwhile Einstein was becoming more famous in academic circles and secured a position in Berlin. So he moved to Berlin, leaving Maric and his sons in Zurich (and continuing to support them).
Around this time he began seeing Elsa Einstein, who was his first- and second- cousin, and who lived in Berlin. Their relationship was loving at first and then sort of evolved into a partnership later in life.
Einstein was still married to Maric for the first 7 years of their relationship. Under pressure from Elsa he finally convinced Maric to divorce him (by famously promising her the proceeds of his Nobel prize which he was widely expected to win). He married Elsa a few months later. Around this time he became a celebrity because the predictions of his general relativity theory (gravitational lensing in this case) were confirmed by astronomers.
As you said, Elsa knew about at least some of Einstein's dalliances. Some of these were probably just friends, but he certainly had some affairs. She seemed to tolerate it for the most part although when he flaunted it she became angry. She and Einstein both seemed to enjoy the limelight associated with Einstein's celebrity, and she acted sort of as a manager in that regard.
Elsa and Einstein fled Nazi Germany in the early 30's and ended up in Princeton at the brand new IAS in 1933. They only lived together there 3 years before she passed away in 1936. Einstein cried as he had reportedly only done once before, when his mother passed away. By all accounts he was very depressed for the next few months, but found solace in his work, and around that time produced a paper on gravitational lensing by galaxies, and on gravitational waves.