Does sin befall one who forgives his brother who wronged him and insisted on shunning him and did not admit his mistake?

You did well by breaking the estrangement with your brother by sending a message of forgiveness and tolerance. You must continue to do so and repel [evil] with what is better, in compliance with the words of Allah Almighty: "And not equal are the good deed and the bad. Repel [evil] with [that] which is better; then suddenly that individual between whom and you was enmity [will become] as though he was a devoted friend." You must continue to reach out to your brother and remember that the older brother deserves respect and appreciation, while your brother must realize that estrangement is impermissible, especially since the mistake was his. Therefore, he must apologize and initiate reconciliation, because the Prophet, peace and blessings be upon him, said: "It is not lawful for a Muslim to forsake his brother for more than three nights, with each turning away from the other when they meet. The better of the two is the one who initiates the greeting of peace."