Your dream seems to reflect the complex emotions and dynamics surrounding your feelings for Brendon and your friendship with Joy. Here are some key elements to consider:

1. Pet Fish: Choosing to buy a pet fish can symbolize a desire for companionship or a new relationship, which aligns with your feelings for Brendon. Fish often represent emotions in dreams, and acquiring one may indicate hope or excitement about developing a connection with him.
2. Forgetting Fish Food: This aspect of the dream suggests feelings of anxiety or inadequacy regarding your relationship with Brendon. It could symbolize a fear of not being prepared or able to nurture a potential romantic relationship. Brendon teasing you may indicate your awareness of his playful side, but it also highlights your vulnerability in this situation.
3. Joy's Presence: Joy's appearance in the dream reflects the complicated nature of your feelings. While you care for her as a friend, her past with Brendon resurfaces feelings of jealousy and insecurity. This may illustrate your subconscious wrestling with the idea of how your relationship with Brendon could be affected by her past involvement.
4. Brendon’s Revelation: His admission about having slept with Joy introduces a sense of betrayal or hurt, mirroring your real-life concerns about emotional connections and past relationships. This part of the dream emphasizes your fears about competition and emotional entanglements.
5. Working at Walmart: This sudden shift in the dream suggests a desire for stability or security. The good pay and hours might indicate a wish to establish your independence or a sense of accomplishment in your waking life. It could also symbolize the idea of working through your emotions and finding a way to cope with the complexities of your relationships.

Overall, your dream encapsulates your feelings of affection, jealousy, and the desire for clarity in your relationships. It may be beneficial to reflect on your emotions regarding both Brendon and Joy and consider how you want to navigate these connections moving forward. Communication might help clarify situations and feelings, especially if you decide to express your feelings to Brendon or talk to Joy about your concerns.