The reason why Cecilia loved Bear in "The Book of Unknown Americans" by Cristina Henriquez can be attributed to several factors:

1. **Personality Compatibility**: Cecilia and Bear might have complementary personalities that resonate with each other. For instance, if Bear is caring, understanding, or supportive, these traits could have connected deeply with Cecilia.

2. **Shared Values**: They could share similar values or beliefs that form a strong foundation for their love. Common values like honesty, loyalty, or kindness can create a deep bond between individuals.

3. **Emotional Connection**: Cecilia and Bear might have shared profound emotional experiences that brought them closer together. Emotional intimacy often plays a crucial role in fostering love and attachment.

4. **Understanding and Acceptance**: Bear might have understood and accepted Cecilia for who she is, flaws and all. Feeling understood and accepted by someone can lead to strong feelings of love and connection.

5. **Chemistry and Attraction**: Physical attraction and chemistry can also play a significant role in romantic relationships. Cecilia might have been drawn to Bear's physical attributes, mannerisms, or charm.

6. **Support and Encouragement**: Bear could have been a source of support and encouragement for Cecilia during challenging times, which can strengthen the bond between two people.

These are some possible reasons why Cecilia loved Bear in the book, but the specific details and nuances of their relationship would be revealed in the narrative, providing a richer understanding of their connection.