Grounded in a critical realist framework, this article examines the habitual and addictive cycles through which social media engagement is produced, sustained, and transformed. Drawing on qualitative interviews with 22 social media users, the study explores how participants experienced and negotiated their relationships with social media across roles as consumers, producers, and prosumers of content. Findings reveal that engagement is shaped not only by individual motivations but also by the interaction of algorithmic recommendation systems, platform business models, visibility cultures, and influencer economies that encourage ongoing participation. Through retroductive analysis, two conceptual models - the habitual cycle and addictive cycle of social media use - are developed to explain movement between routine and compulsive forms of engagement. The models demonstrate that users shift between these modes under changing social, cultural, and platform conditions rather than occupying fixed categories of either habitual or addictive use. The article further shows how experiences commonly described as addiction emerge from underlying structural and cultural mechanisms that encourage continual engagement whilst simultaneously individualising responsibility for its regulation. It argues that understanding social media harms requires attention to the relationship between user agency and platform structures, shifting analysis beyond individual behavioural explanations towards broader questions of platform governance, prosumption, and social harm.