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It sounds like you may have the wrong cherry type for your area. Your climate is most equivalent to our USDA zone 9, which there aren't many cherry cultivars that do well there. It doesn't get cold enough, or stay cold enough for most cherry trees to flower, properly.

This problem will likely not be resolved unless another cultivar is chosen for the spot.

Here is an article that will help you understand the cooling requirements for cherry trees:

https://www.gardeningknowhow.com/edible/fruits/cherry/chill-hours-for-cherries.htm

It looks a little young to prune, but if you must, I would only take the top inch off of each main branch. There is no real reason to do this yet, and doing so poses a risk of infection, though.

This article will help you to know how and when to do so:

https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-pruning.htm

Unfortunately, your photo did not come through. There are many fungi, bacteria, and viruses that can affect cherries, and it can be very difficult to diagnose with description alone.

While some diseases are curable, some are not. Here are some articles that will help:

https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-diseases.htm

https://www.gardeningknowhow.com/edible/fruits/cherry/witches-broom-of-cherry-trees.htm

https://www.gardeningknowhow.com/edible/fruits/cherry/treating-cherry-leaf-spot.htm

This is very unfortunate. It appears to be the early symptoms of Ganoderma rot. This is untreateable, even in early stages. You can expect the tree's fast decline in 5 years or less.

When the fruiting bodies form, they still have some use. All forms of Ganoderma posses medicinal qualities.

Here is an article with more information:

https://www.gardeningknowhow.com/ornamental/trees/tgen/ganoderma-root-rot-disease.htm

In the photo, the tree appears to be alive. It does appear to be infected from overwatering, or the soil has not had a chance to dry out enough to keep the tree healthy. This will cause root suffocation, and disease.

I would treat with a fungicide or bactericide.

Here are some some articles that will help:

https://www.gardeningknowhow.com/garden-how-to/info/using-fungicides-in-garden.htm

https://www.gardeningknowhow.com/special/organic/biofungicide-information.htm

https://www.gardeningknowhow.com/garden-how-to/info/homemade-fungicide.htm

https://www.gardeningknowhow.com/garden-how-to/info/applying-bactericide-to-plants.htm

These articles may help:

https://www.gardeningknowhow.com/edible/fruits/cherry/cherry-tree-diseases.htm

https://www.gardeningknowhow.com/plant-problems/disease/black-knot-tree-disease.htm

https://www.gardeningknowhow.com/edible/fruits/cherry/x-disease-in-cherries.htm