Tree looks like it has Black Canker, a common disease of willow trees.  The black spots on the leaves as well as the black on the stem (the canker) and the thinning/die back in the canopy are signs I can see in the images you provided.  

Unfortunately, this is not a disease that we have chemicals that can cure it.  In trees that are not heavily infected you can rake and destroy the infected foliage and cut out the diseased branches.  But based on the dieback in the tree, this is likely not possible in your tree.  The stress from the summer droughts may have made the problem worse.  

Here is some information about it: https://www.montana.edu/extension/pubs/a-guide-to-pests-problems-and-identification-of-ornamental-shrubs-and-trees-in-montana/diseases/black-cancer-of-willow.html 

Thank you very much for your response. So does that mean it is unlikely it will survive? Could you possible recommend next steps? I would really like to treat it/ save it, if possible. Thank you in advance. 

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It may survive for several years as parts of the crown die out. You can remove those portions as they die out.  There is no cure or treatment for it.