Hi Mike, 

Sorry to hear about your tree.  Based upon your photos and the information you shared with me, your oak appears to have oak leaf blister. https://planttalk.colostate.edu/topics/insects-diseases/1449-oak-leaf-blister/

This is a fungal disease.  The fungus survives on dead leaves and on the crevices of the bark and on the buds.  When the buds open in the spring, the leaves become infected.  Once they are infected, there is no treatment, unfortunately.  The tree will need to be sprayed next spring before bud break to prevent infection next year.   

In the meantime, try to give you tree some TLC.  If 50% of the leaves are affected, the tree could become severely stressed this summer.  Watering too much can be as bad as watering too little.  You should check the moisture of the soil to be sure it is not saturated before additional watering.  Fertilizing is NOT warranted either.  It isn't necessary.  

In addition, I recommend you water your tree this winter.  Trees, in fact your entire landscape, may need additional water next fall and winter.  They need about 1 inch of water per month.  If not, you'll need to add supplemental water.  Here's a fact sheet on Fall and Winter watering.  https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/

Finally, here's some information on arborists.  I would suggest hiring one to spray for the oak leaf blister next spring before bud break.  There is nothing that can be done this summer, unfortunately.  https://www.treesaregood.org/findanarborist

Sorry for the bad next.  Hopefully, your tree can make a come back.  Let me know if you have further questions.