The boy sent a sentence "I just want to be quiet" to the girl, and then he made a smiling and crying expression. What does this mean?

He's joking with you. It was a joke to say that I just wanted to be quiet, which is already a well-known funny online expression. It doesn't really mean quiet. Later, the boy gave you a smile and cry expression, further indicating that he was joking with you, but found that you seemed to take it seriously, so he used this expression and didn't imply anything else. You just need to be a joke. There is no need to be serious and think too much. Happy every day!