Μοιχάω or μοιχεύω (in Modern Greek) is simple present tense and means to commit adultery. In Mark 10:12 is used the form μοιχᾶται, which is the original type (before transliteration).
According to Mark 10:12, yes, if a woman divorces her husband and marries another one, she commits adultery. The simple present tense shows duration and describes a stable action.
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.