Erica Albright broke up with Mark Zuckerberg just because in a small, tiny thing. Also, Erica doesn’t want Mark to underestimate her. By letting him introduce Erica to his new friends when he gets a new club on Harvard to let him be popular.
2. How did Mark betray Eduardo? As shown in the film what happens is that Mark dilutes Eduardo's stock in Facebook. Zuckerberg, Parker, Saverin, and Moskovitz all had significant segments of Facebook stock along with investor Peter Thiel. Increasingly dissatisfied with Eduardo, Mark decides to push him out of the company. To do so he does a major stock issue, increasing the total number of shares of Facebook stock available. While he, Moskovitz, and Thiel all get more shares of stock, Eduardo retains the same number of shares he originally had. Since there are more overall shares this means that Eduardo controls far less of the company than he did originally. Eduardo's share of the company went from 33%, second only to Mark's 51%, down to an insignificant 0.03%, effectively removing him as a power within the company. This enraged Eduardo and he sued Mark, settling for an undisclosed amount of money out of court and having his name restored as co-founder of the site.
3. Did Mark really do all the things Eduardo implied he did in the confrontation?
This is never explicitly stated. But in a way, the point of the film is not to explain these things directly. This is shown in the final scene where Marilyn, the junior lawyer on Mark's team explains to him how easy it would be for her to win the cases against him, she mentions how she doesn't have to prove anything, just ask the right questions that people will form the answers to in their own minds regardless of what he says. This is very much the trick the film uses too when it's making more serious implications about the actions of the