You don't have to live in the same town or — or even the same country — as your best friend to maintain a strong friendship. Even so, it can be challenging to live far away from your favorite people.

Dear Amy: “Mary” and I have been very close friends for 50 years. We are both conflict-averse, so have had very few “bumps” along the way, but when they happened, we were able to move on. Last year, ...