What would you do?

I recently met someone who is currently teaching in Cambodia. I won’t mention the name of the town, as it’s a very small place and my intention is not to point fingers. This individual is living with a partner who has a questionable past and has overstayed their visa by eight or nine years. As a result, the partner cannot legally work in Cambodia. I also discovered that this partner has been purchasing drugs using the money earned by the teacher, all while we frequently hear about the financial struggles their family is facing.

I'm wondering what the best course of action would be in this situation. Am I legally obligated to speak with the immigration or tourist police and have this person investigated? I've also heard that he is volunteering at schools specifically to avoid showing his passport, which is particularly concerning to me. Several people have tried to encourage the teacher to leave him, since he seems to be a negative influence, but he manipulates her and turns her against those who want to help. Could the teacher face any consequences for allowing someone who is living in the country illegally to stay with her? I'm really just looking for advice about this situation. I don't plan to take any direct action, but it's been weighing on my mind and I can't seem to let it go.