1911 was a busy year for Russell. He lectured at Trinity College, became president of The Aristotelian Society, wrote essays on popular philosophy, proofread subsequent volumes of Principia Mathematica, courted Ottoline Morrell, split with Alys and met Ludwig Wittgenstein.
Early in the year, he spent an evening alone with Ottoline, and although they didn't consummate their relationship then, they planned to pursue one. Ottoline had an open marriage with her husband, Philip, and they lived together with their daughter. Ottoline was slow to reveal facts about herself, and Russell wasn't exactly quick to catch on. She was in the process of breaking off an affair with the artist and critic Roger Fry and was continuing one with the artist Henry Lamb. Initially, Russell naïvely insisted that she stop having sex with her husband. He also suggested that they could have a child together, not knowing that she had already had an operation to prevent pregnancy. Alys's brother, Logan, became enraged when he heard about Ottoline and Russell's affair, and, with Alys, informed him that Russell and Alys could remain separated and not divorce as long as Russell never stayed in the same building as Ottoline. This marked the end of Russell's relationship with Alys, though, apparently, she continued to love him for the rest of her life.
Russell's relationship with Ottoline seems to have been problematic from the start. Obviously he had made a serious mistake by marrying Alys, but there is little evidence that he reflected on that mistake and arrived at a better alternative. I think that Alys was a rather ordinary American woman, and that Russell probably wasn't aware of the relevant cultural differences. She had a predictable do-good Quaker orientation with little interest in ideas per se. Ottoline was an improvement in the sense that, like Russell, she was an English aristocrat and was not explicitly interested in having a positive impact on mankind. However, she had a highly developed personal sense of religion which Russell attempted to argue away. Though he correctly believed that the Christian God does not exist, he rather insensitively forced his ideas on Ottoline and persuaded her to read Spinoza, something that she never would have done on her own. Ottoline was above all a high-society woman and a patron of the arts: she was not especially intellectual and understandably had no interest in arriving at a logically consistent and accurate view of the world. My guess is that she was dazzled by the attention of someone with Russell's intellect, but that alone was not enough to sustain a lasting relationship. To make matters worse, she was not physically attracted to him. By early 1912 she seemed stressed out by her relationship with him and seemed ready for a change.
Ludwig Wittgenstein had been studying aeronautical engineering in Manchester but was losing interest in it. He read The Principles of Mathematics, became interested in mathematical logic and visited Gottlob Frege, who suggested that he study with Russell. He descended on Cambridge and followed Russell around, aggressively engaging in arguments. At first, Russell thought that he was a demented eccentric. However, at that time hardly anyone attended Russell's lectures, and Russell became impressed by Wittgenstein's intellect. By then, Russell associated his mathematical work with depression, because his serious works were all written when his relationship with Alys was in a dismal state. His relationship with Ottoline seems to have lowered his opinion of formal philosophical work, and he was starting to think that academic philosophy wasn't all that important. Wittgenstein played into this, because he was able to understand Russell's work without any formal philosophical training. This was the beginning of Wittgenstein's illustrious career as a philosopher, and I am once again surprised to see how personal bonds that originated in a haphazard series of events made it possible. This arrangement may have worked for Russell, because later on it permitted him to ease out of academia by replacing himself with his protégé.
The Aristotelian Society hosted Henri Bergson, then a famous French philosopher. For the occasion, Russell read Bergson's works and didn't think much of them. I often find it interesting to see how divergent British and French culture are, when you consider their long history as neighbors. The British have historically seemed willfully ignorant of French culture, and the French, perhaps accurately, have seemed to consider the British crude. When you recognize that the Norman conquest was a seminal event in British history, it is a little surprising how different the two countries seem today.