be at the end of (one's) tether

To be completely worn out, exasperated, or exhausted; to have no more patience, endurance, or energy left. The baby's been crying all morning, and I haven't slept properly in days! I'm just at the end of my tether! The bosses are at the end of their tethers with the way this project is moving, so they've decided to bring in some outside help.

be at the ˌend of your ˈtether

(British English) (American English be at the ˌend of your ˈrope) having no more patience or strength left: After two hours of hearing the children shout and argue, I really was at the end of my tether.