The Talmud (Megilah 13A) does not reference the Hebrew word for wife, but the Hebrew word for someone in the inner family circle. In this regard, the Talmud here draws the comparison to 2 Sam 12:3, where Uriah the Hittite had groomed young Bathsheba to be his wife. The Greek Septuagint therefore translates the passage here in Esther as follows:
When her parents died, he [Mordecai] trained her [Esther] for himself as a wife.
Mordecai therefore did not take her as a wife, but took her into the inner family circle with the intent to groom and nurture her as she became older. Thus, at this time in the story, the description by Josephus (Antiquities of the Jews, Book 11, Chapter 6), the three separate Targumim of Esther, and the received Masoretic Text all indicate the relationship between Mordecai and Esther was like "father and daughter" rather than a consummated relationship between "husband and wife," which of course may have occurred later had not the story of Esther taken a twist.