It's important to approach situations like this with caution and consider the potential implications for all parties involved. Meeting someone's child, especially in the context of an affair, can be a complex and delicate matter. While the specific reason for his request can vary depending on the individual and their circumstances, here are some potential reasons other than being referred to as a "best friend":
Introducing you as a significant other: It's possible that he sees you as more than just a friend and wants to integrate you into his personal life as a romantic partner.
Seeking approval or validation: He may want his daughter to meet you to seek her approval or gauge how well you get along with her, as her opinion may carry weight in his decision-making.
Building a closer bond: Introducing you to his daughter could be an effort to deepen the emotional connection between you and him.
Testing the waters for a long-term commitment: He might be considering the potential for a more serious and committed relationship and wants to observe how well you interact with his daughter as a way of assessing your compatibility for a future together.
Normalizing your presence: By introducing you to his daughter, he might be trying to make your involvement in his life more normal and acceptable to those close to him.
It's essential to be mindful of the situation and recognize the potential consequences of being involved with someone who is in an affair. If either of you is in a committed relationship or marriage, it's crucial to consider the impact on the other party and their family as well.
Before agreeing to meet his daughter or progressing further in the relationship, it's essential to have open and honest communication with him about your feelings, expectations, and the implications of your involvement. Additionally, it might be wise to seek the advice of a professional counselor or therapist who can provide guidance and support in navigating this complex situation.