I want to focus on the act four.
After the three of them come back home from Embassy, everybody is tired, especially Eliza. She has kept in a state of tension through the whole party, and she even have to behave naturally like a lady without revealing her being nervous. I think it is quite difficult for her; she still makes it, though. As a matter of fact, her performance is really admirable. Just like Pickering has said," You have not lost it, my dear. You have won it ten times over ", this success means not only Eliza wins the bet for Higgins, but also Eliza's own victory. She has made a great change of her fortune whether it will become better or worse. Anyway, it is absolutely worthy of celebration. Although she is very weary, I think she must be going to exclaim about her success, share the feeling of excitement or strain with these two men, and maybe she will give them a big hug if the two men's attitude is different. Eliza has no time to show her feeling to them but hears their response toward it first. What a cruel blow to her! Their reaction is just contrary to her expectation. To Eliza's most heartbreak, she finds out how she is truly regarded in Higgins's mind. She seems a heavy burden to him, at best a secretary remembering his appointments and trivia for him occasionally. She obtains a lot of pleasure from learning, but he doesn't. What he thinks is hoping everything gets over as soon as possible. It really hurts. I don't think it is Higgins's rudeness that results in Eliza's leave. Because she should have accustomed to it for so long a time since she came to his house in the very beginning. His bad temper or the way he treats her influences her little. No matter how he abases her by calling her creature or insect, she doesn't take it seriously. I think the moment she realizes that Higgins doesn't want to involves with her emotionally she decides to give up the hope. She must be disappointed and deeply hurt. Otherwise, when Higgins says he is wounded to his heart by the words she said, Eliza should feel apologetic rather than being complacent. Another possible factor is that Eliza finally understands it is hard to communicate with Higgins. There is much difference between their thoughts. Eliza is a woman of dream and ambition. She won't let her life under someone's control. So, leaving is sensible to her. It is very strange that once they get married, she may put up with all of his erratic manners. If they just keep in a simple relationship, she can't help but criticize or complain about him at any time. However, it seems that all couples are in common in this situation.