Walden by Amy Berryman

Set in the near future, when we have depleted Earth's resources and NASA has begun "colonizing" the Moon, Stella and Cassie meet for the first time in years. But this is no ordinary reunion - these fraternal twins have been separated by more than just years and miles. And in her absence, Stella has begun a new life with her fiance, Bryan - an Earth Advocate who's devoted his life to saving what parts of Earth we still can. Over a single weekend, the trio work to find connection and healing after an undefined rupture that constantly threatens to rear its head.