He read my message and didn't reply

Sophia, when you care and get angry, that is a response to your unfulfilled expectations. For example, the OP expected him to answer her message in timely manner. For her, that timely manner was around 4 hours. After those 4 hours she was feeling anxious, annoyed and angry. All these were not because of him not responding. It was because she EXPECTED him to answer in less than 4 hours.

When you begin shifting your thoughts like this you will start to see your own triggers and what your expectations are. And you understand it is not the other person’s fault. People can act however they like, you cannot control that. But you can control your reaction to their behavior. And then you start to assume responsibility for your feelings and learn not to expect people to behave in a certain way. This is where “happy but indifferent” attitude comes from