I’m having a conflict with one of my colleagues. It’s really stressing me out. We have tried everything to resolve the dispute, but nothing has worked. I’m at the end of my tether (am Rande der Verzweiflung)
A tether is a long rope tied to a post or a tree that allows an animal to move in a circle only so far from where the tether is tied. In fact, the more common form of the idiom in the US is „at the end of your rope“. To be at the end of your tether or rope means that you can go no farther.