In Endangered, by Eliot Schrefer, Sophie is afraid of losing Otto because her deep loving relationship with him is the proof of how much she cares for bonobos and their safety,
When she arrives to the Congo to stay with her mother, she actually buys a bonobo from a man with the intention of saving it from slavery and the horrible conditions they were living in.
Then she realizes that by buying Otto she contributed to the black market, but she had already developed a profound relationship with Otto and had saved him, so she couldn't really regret the purchase.
Sophie is afraid of losing Otto because she truly loves him and is decided to help him and all the other bonobos to be free and safe.