What is going on with my tree? I believe it is an ash tree. It has suddenly...
What you are seeing is most likely ash anthracnose, which will cause leaf drop:
Anthracnose is common in cool, wet springs. Generally, no control is necessary (nor possible at this stage). Healthy deciduous trees can withstand two or three years of defoliation without serious harm, and the anthracnose won't completely defoliate your tree.
It also looks like there is also some insect activity (wooly aphids along the stem of the leaf, and perhaps some insect egg clusters) and perhaps some leaf galls:
But the anthracnose is the more serious problem.