My experience for language exchange friends I'll share how yo keep communication with my language exchange friends.
To be language exchange friends is really easy, but suddenly they might disappearfrom you.

In my experience, the balance between two languages is very important.
If either one speaks only one which the person study, the other person must have complain. For me, just talking for long time is kind of wasting of time, so I always try to teach something about Japanese each conversation.

But if someone suddenly disappeared, the person might find other language exchange friends better than you, so we always have to pay attention to take care to communicate to them more.