It means that he is loyal to someone and constantly strives to contribute to someone. (implication: I also expect someone to take care of his heart. However, some people misunderstood his efforts and didn't see him that way at all. This made him feel sad and angry.
A person with lofty ideals and kindness can't complain. It has been difficult to use talents since ancient times.
It also expressed his resentment and resentment that he was not reused by the court.
Must be a poem? Generally speaking, ancient poems do not directly express the emotion of "anger", which is rather hazy.