Q.What is the pink fungus on my pussy willow?
What is the pink fungus on my pussy willow? I was outside and took a look at my pussy willow tree and saw a pink fungus on the leaves.

It's hard to make a clear diagnosis from your description.
Pussy Willow does not usually have issues with disease or insects.
Powdery Mildew is a possibility and I would recommend treating it with Neem Oil. Neem Oil works as both a fungicide and pesticide.
https://www.gardeningknowhow.com/ornamental/shrubs/pussy-willow/growing-pussy-willows.htm
https://www.gardeningknowhow.com/ornamental/shrubs/pussy-willow/growing-pussy-willows.htm