This dream is rich with symbolism and seems to reflect various aspects of your life, emotions, and potentially your relationships. Here are some interpretations that might resonate with you:

1. Grandfather and Nostalgia: The presence of your grandfather, whom you haven't seen in years, suggests a longing for connection or a desire to revisit your past. It may also symbolize wisdom and guidance as you navigate your current situation.
2. The Mysterious Man: The guy at the party who is different from your partner may represent the allure of something new and exciting in your life. This could symbolize a desire for change or exploration outside of your current relationship.
3. Floating and Dancing: Floating in the air and dancing signifies a feeling of freedom and joy. It may indicate that you have moments in your life where you feel carefree and happy, contrasting with the more serious aspects of your dream.
4. Feeling Out of Control: The transition from having fun to feeling trapped in the man's car and heading in the wrong direction reflects feelings of losing control over your circumstances or decisions. It could symbolize anxiety about being led astray or making choices that don't align with your true desires.
5. Oat Milk and Comfort: The references to oat milk and coffee might symbolize your need for comfort and routine. The insistence on having oat milk could represent your boundaries and preferences in relationships. It suggests that you have certain needs that must be met for you to feel at ease.
6. Ex and Emotional Ties: The appearance of your ex and the message about "no us without you" could indicate unresolved feelings or nostalgia for past relationships. It might suggest a struggle between moving on and holding onto what was.
7. Shop and Choices: The convenience store filled with cheesecakes symbolizes temptation and the variety of choices available to you. The contrast between the outside and inside of the store may reflect how things can appear different than they are—an important theme when making decisions.
8. Sean and Help: The character 'Seanie Boy' could represent the support you may need or seek from others in your life. It suggests that you're looking for assistance in meeting your needs, both emotionally and practically.

Overall, this dream seems to explore themes of freedom, control, emotional needs, and the complexity of relationships. It may be beneficial to reflect on your current feelings about your relationship and any unresolved issues from the past. Consider what comfort and support you truly seek in your life and whether those needs are being met.