I am always with you yet I am not there, I am your closest friend was worst of enemies, even when alone you'll find me close, I am the one who has been with you most.

The answer to the riddle is loneliness, a complex human emotion that resonates deeply with each clue. It is an internal state, a feeling of distress or discomfort arising from a perceived gap between the social connections one desires and those one actually experiences. This explains how it can be "always with you yet I am not there" – it's a subjective experience, not a physical presence, and can persist even when surrounded by others.

This paradoxical feeling can indeed be "your closest friend was worst of enemies." As an "enemy," chronic loneliness is linked to significant negative impacts on mental and physical health, including increased risk of depression, anxiety, heart disease, and even Alzheimer's disease. It can trigger stress hormones and disrupt sleep. Yet, in a strange way, confronting loneliness can also force introspection and self-discovery, pushing individuals to understand themselves better, thus becoming a catalyst for growth, much like a challenging "friend."

The phrase "even when alone you'll find me close" directly points to the core experience of loneliness, often felt most acutely in moments of solitude. It is important to distinguish loneliness from solitude; while solitude is a chosen state of being alone that can be peaceful and rejuvenating, loneliness is an unwanted feeling of isolation, regardless of whether others are physically present. Finally, "I am the one who has been with you most" reflects the pervasive nature of loneliness as a fundamental human experience that can occur at any age and recur throughout a person's life, making it a constant, albeit often unwelcome, companion.