Dreams involving ex-partners, particularly those that evoke strong feelings like jealousy and anger, can often reflect unresolved emotions or conflicts from the past. Your dream appears to highlight feelings of insecurity and betrayal, especially since you envisioned your ex being flirtatious with someone who represents a part of her past.

The presence of an unknown man as a substitute for your best friend could symbolize a fear of losing your current support system or feeling replaced. The escalating situation, where you find your ex being intimate with this man, may indicate anxieties about your past relationship and a fear of being vulnerable or inadequate.

Your aggressive reaction in the dream—dragging her by the hair and confronting the man—suggests that you're grappling with feelings of powerlessness or a desire to regain control over your emotions and circumstances. It may also reflect a part of you that is still protective or possessive regarding your ex, despite the relationship being over.

Overall, this dream may be prompting you to examine any lingering feelings about your past relationship and how they affect your current emotional state. It could be beneficial to reflect on what aspects of the past you need to confront or let go of in order to move forward in a healthier way. Consider discussing these feelings with a trusted friend or a counselor, as it may help in processing them.