atanakar
Hero
Yeah, I pretty much have to be the DM or the group likely fades away. And getting groups of players who aren't bleeps in a town of under 4k isn't just hard, it's a process that takes years.
It seems unfair to you if they only come to play but never want to shoulder part of the effort, from time to time. It doesn't need to be a full campaign. The alternate GM can run just a short module or even one session. When I am tired I leave my seat for a session or two. The other GM makes us try a system we don't know.
If you burn out fully they loose everything. Is that what they want? Have you talked about this with the group?