Shisui's decision to take his own life is indeed heartbreaking. He was deeply troubled by the fate of his clan and chose to protect them from ongoing despair. He felt responsible for preventing further conflict and believed that his death would empower Itachi to take a stand against the Uchiha's dark path.
It's a tragic sacrifice, showing how much he cared for his friends and family, even in his final moments. He wanted to ensure peace, even at the cost of his own life, which reveals the depth of his character and the heavy burdens placed on him throughout the series.