In conversation, the simple past and the past perfect are both acceptable, and it really doesn't matter how many times you met them over that month. The difference is that, if you use the simple past, you are expressing both your meeting them and the divorce relative to the present. If you still feel the shock, for instance, that might be quite natural. If you are trying to paint a picture of how you felt in that moment when you learned of the divorce, the past perfect is what you want. The simple past keeps the user in the present, thinking about two past events. The past perfect places the user at the moment of your learning of the divorce, and thinking about the earlier event as being in the past at that point.
I say "In conversation" because, in writing, you tend be in the storytelling mode where you put the reader at the time of the past event you are talking about. In speech, you are in the present with your listener, although you can still "place them in the past" with the past perfect.