If you miss someone who’s still alive, that’s not sad. That’s a phone call waiting to happen.

Missing someone gets treated as a feeling to sit with, when often it is information about an action you have not taken. Distance between two living people is usually maintained by both of them, out of awkwardness rather than anything serious. Neither one wants to be the first to reach. So the gap holds, and both sides quietly call it drifting apart.

If a name arrived in your head just now, message it. No explanation is needed and no occasion is required. The most useful opening line is simply saying that you were thinking about them.