Complex sentence: Mr. Ping admits to Li that he was initially worried Po would be taken away from him, but came to realize that Li being a part of Po's life simply added to his happiness, and that they must stay by his side.
Split into simpler sentences: Mr. Ping admits to Li that he was initially worried Po would be taken away from him. He then realizes that being a part of Po's life was what made Po happy, and they must stay by his side.