You got of at Mainz-Kastel which is on the other side of the Rhine. Mainz-Kastel was a suburb of Mainz but after WWII when the Rhine became the official border between the US and French Zone Mainz-Kastel was given to Wiesbaden and is officially now a suburb of Wiesbaden.

According to the map they probably split at Bischofsheim which is the last stop before their routes split.