Meaning of since

Does the highlighted "since" mean "from the time that" or "because and as"?

Context:

But as Eve Kosofsky Sedgwick uses it in her important book on queer theory, Epistemology of the Closet (1992), the term “closet” becomes a critical tool that allows for the investigation of homosexuality and heterosexuality as the most important culturally constructed categories in twentieth-century intellectual history. Sedgwick uncovers and questions the heteronormative categorization of homosexuality in her study of certain canonical authors ofmodern literature, along with its delineation of the “homo/heterosexual definition.” She concludes that this definition is highly contradictory and unstable. The “relations of the gay closet,” as she calls them—silence and/or secrecy, and even the social deception regarding the gay man’s sexuality and relationships, and the threat of stigma and bias that forces the perpetuation of a cycle of secrecy about one’s identity, at great psychic cost—typified homosexual daily life and culture in modern Western society until the watershed event of the Stonewall riots of 1969 in New York City’s West Village, after which the gay-rights movement became much more confrontational. Sedgwick draws on key authors who contribute to the debate on the homo/heterosexual definition, including Herman Melville, Oscar Wilde, Henry James, and Marcel Proust. Since Sedgwick took up the gay closet as an issue relevant to Western culture and to queer theory, art historians such as Kenneth Silver have examined visual artworks that similarly engage with the strictures of closeted gay existence during the pre-Stonewall period.