From Longman Dictionary of Contemporary Englishbe at the end of your tetherbe at the end of your tetherFED UPto be so worried, tired etc that you feel you can no longer deal with a difficult or upsetting situation → tether
Examples from the Corpus
be at the end of your tether• I had no money, my husband was sick, and I couldn't get a job. I was at the end of my tether. 