In this part of the story, Mowgli is expressing a mixture of sadness, defiance, and a sense of betrayal. He feels a deep connection to the wolf pack and wishes to remain one of them, but he recognizes that he is being seen as different because he is a human. His declaration that he will no longer call the wolves his brothers signals a painful acceptance of his identity as a man, which causes him distress.
The cause of Mowgli's feelings stems from the conflict between his upbringing in the jungle and his true nature as a human. He has been raised by wolves and feels a strong bond with them, yet the wolves' insistence that he is a man creates a rift. This internal struggle is compounded by his desire for belonging and love from the pack, alongside the reality that he must navigate the complexities of his dual identity. The combination of his love for the wolves and the acknowledgment of his human status leads to feelings of isolation and loss.