Weeping cherry tree
Thank you for your question about your cherry tree. It would appear from the photos of the leaves that your tree is infected with the cherry leaf spot fungus, which is common in the Willamette Valley. Here is a link to an article that describes the fungus, and provides suggestions for cultural (raking, destroying leaves) and chemical controls. One of the chemicals, Bonide Captan, is available to the home gardener, but the fungal spores are already proliferating, the damage has already been done to the leaves, and it is too late in the season for application. So, preventing the fungus from recurring next year is really your only hope. (This assumes the tree survives the year.)
Begin your raking and disposal of the leaves now and throughout the season as they drop, so the fungus does not overwinter. Here is a link to another more thorough explanation of diseases that you might find helpful; cherries are on page 7.
I'm sorry there is not more encouraging information for this year. Hope these are helpful. Good luck!