What is your advice to me regarding how to stop speaking with immodest girls in Australia—which sometimes reaches the point of flirting—given that I am unable to get married?

A caller to Allah must be the most diligent of people in obeying Allah and avoiding His disobedience, especially the temptation of women. This is based on the Prophet's (peace be upon him) saying: "I have not left behind me a temptation more harmful to men than women." The jurists have stipulated the prohibition of speaking to a non-mahram (definition) woman without need, because it is a source of temptation. One must lower the gaze, and hasten to marry when able. If not possible, then patience, self-restraint, keeping good company, and frequent supplication are necessary.