Dreams involving relationships, especially those that include ex-partners, can often reflect underlying feelings of insecurity, jealousy, or concerns about fidelity. In your dream, seeing your wife with her ex-husband may symbolize fears of emotional distance or a perceived threat to your relationship. The detail of her mentioning needing "six" men may suggest feelings of inadequacy or questioning your role in her life.

The act of your wife's ex returning with watermelons could symbolize abundance or choices, as watermelons can represent fertility and growth. The instruction to "pick one" may indicate a dilemma or decision that you or your wife is facing in real life.

The connection to the Stevia packet's message about picking the "fun one" may suggest that you need to focus on making choices that bring joy and satisfaction rather than dwelling on fears or insecurities.

Overall, this dream might be encouraging you to communicate openly with your wife about any feelings of insecurity or concerns you may have, as addressing these issues can help strengthen your relationship. Additionally, consider what choices you are facing in your waking life and strive to choose paths that resonate with your happiness.