Bernardo and Anita actually pretty much agreed about living in America versus living in Puerto Rico. Contrary to what Bernardo said, he was happy be in America, especially in New York City. Puerto Rico was an economic dead-end and nowhere near as fun for a early twenty something as New York City. Contrary to Anita's bravado, she really did feel discriminated and threatened by White America.
However, Bernardo and Anita would never admit that they basically agreed. They enjoyed the fire of arguing too much, especially if they could argue through dance and then have the most passionate sex, practically dancing and fighting their way through the love-making.
However after Bernardo died, Anita hated herself never telling Bernardo that she understands why he was so angry at America, so threatened on the streets, had such antipathy for the white gang. Because after that fateful night of the rumble gone very wrong, Anita felt that hatred in her heart and then some.
Anita had some distant liking for Maria before the events of West Side Story took place. Anita did think Maria was adorable and sweet and she wanted to get on the good side of her likely future sister-in-law. However, she didn't really care that much about Maria as a person. She really only briefly defended Maria's right to flirt with Tony at the dance to toy with Bernardo.
During the events in the main of West Side Story, Anita became increasingly frustrated with Maria. Rejecting Chino, betraying her brother. The girls at the sewing shop thought Maria's "I Feel Pretty" was just *adorable* and didn't mind cleaning up after Maria's mess that she made of the shop. Anita thought it was ridiculous that Maria was apparently old enough to break her brother's rules and have big time sexual tension (and later sex) with a Pollack but she wasn't grown-up enough to clean up the messes from her own song and dance numbers but left Anita and the other girls to do it (right when Anita had to dress for a very important post-fight date with Bernardo!).
By the time that Anita found Maria with Tony right after Tony killed Bernardo, Anita thought that she really had it with Maria. Now, Maria's explanation of how her genuine her love for Tony was made Maria pitiable enough to Anita for Anita to warn Maria that Chino had a gun and was heading after Tony. However, Anita imagined that she would just do this good deed to save Maria the same pain of having her first love murdered and hopefully, Maria would just marry the Pollack and Anita wouldn't have to deal with Maria again. Anita's silence during Maria's "I love Him" was pity and feeling too exhausted to argue. It sure wasn't *approval*.
After Tony died, Anita felt true simpatico beyond pity for Maria. It was partly because the tragedy changed Maria. Maria came out of the experience retaining her love for Tony but gaining a new hatred for the white gang for nearly raping Anita, dragging Tony into their gang warfare, prompting Bernardo into the white gang's game of turf wars in New York City.
Anita and Maria bonded over losing their loves. Anita felt guilty for spitefully delivering the wrong message to the Jets that Maria was dead which caused a heartbroken Tony to go out looking for death. Maria felt guilty for instructing Anita to deliver a message to Tony and thus, put Anita in the "Jet's enemy camp"
Both women carried such terrible burdens of loss and unfair guilt that Maria and Anita became unlikely best friends and sisters for rest of their lives. Anita and Maria both wondered to themselves if they could have ever become so close if they weren't bonded through tragedy and hatred and guilt. If Anita ended up with Bernardo and Maria ended up with Tony, wouldn't they have likely just drifted apart? However, Maria and Anita both never discussed those feelings because it was just too unbelievably painful and....awkward for lack of a better word to bring up to the other one. For years, they mainly talked the seamstress business, their future husbands and kids, everything except what happened that fateful night of the rumble to draw them closer.