This dream is rich with symbolism and seems to reflect various aspects of your life, particularly related to your past experiences, relationships, and perhaps feelings of conflict or nostalgia.

1. Old Elementary School/High School: Returning to your old school can symbolize a journey into your past. It may represent unfinished business, unresolved feelings, or a desire to reconnect with your childhood self. Schools often represent learning and personal growth, so this could indicate a phase of introspection or a need to revisit lessons from your past.
2. AP Psychology Class and Teacher: The shift from a familiar teacher to a new, attractive figure could indicate a desire for change or new perspectives in your life. The fact that the teacher is a middle-aged woman may represent wisdom or nurturing qualities that you are seeking or need to explore. Your flirting could symbolize a desire for emotional connection or validation.
3. Conflict with Classmates: The frustration from your adult classmates about not participating in the group project may reflect feelings of guilt or anxiety about not contributing enough in certain areas of your life. It could also point to concerns about how others perceive your actions or priorities.
4. Intimacy with the Teacher: This part of the dream suggests a conflict between desire and social expectations. The secluded setting indicates a longing for intimacy or connection, while the fear of being seen suggests concerns about judgment or the consequences of your actions.
5. Friend Nate and the Construction Site: Nate's appearance could symbolize friendship or support in your life. The construction site may represent transition or growth, as it’s a space that is still being formed. It could indicate your current state of mind, where you are building or reconstructing aspects of your identity or life situation.
6. Looping Back to Class: The cyclical nature of the dream suggests that you may feel stuck in certain patterns or experiences. It could imply a need to break free from these recurring themes in your life or to learn from them.

Overall, this dream seems to reflect a complex interplay of nostalgia, desire for change, social pressures, and personal growth. Consider what aspects of your past or current life you might be grappling with, and how they connect to your feelings of intimacy, responsibility, and self-identity. It may be beneficial to reflect on these feelings and how they influence your present life and relationships.