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It sounds like peach borer. This article will help you:
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-borer.htm

Check the lable on the tree before you purchase. Most spcies are self pollinating, so you'll only need one.

What you're describing sounds like a fungal infection, possibly brown rot? Check with your local extension office (found under gov't in your phone book) for advice on the best way to treat these type of infections, specific to your area.
I normally use copper sulfate as a fungicide on my fruit trees, but I have no peaches. The borers won that one, LOL

Thank you for sending us your question. The following article(s) should be of some help to you: https://www.gardeningknowhow.com/plant-problems/pests/keeping-ants-of-flowering-vines-vegetables-and-flowers.htm

https://www.gardeningknowhow.com/plant-problems/pests/insects/get-rid-of-ants.htm

This sounds like a combination of problems, the high heat is causing a lot of stress to the tree, which is probably one of the reasons it's dropping leaves. When you water a peach tree, try to water deeply once a week. Don't try to add fertilizer when it is doing this.
Here are a couple of articles that may be of help to you:

https://www.gardeningknowhow.com/edible/fruits/peach/common-peach-diseases.htm
https://www.gardeningknowhow.com/edible/fruits/peach/peach-tree-care.htm

This article may be of help:

https://www.gardeningknowhow.com/edible/fruits/peach/common-peach-diseases.htm

And I also suggest you contact your local extension office (found under gov't in the phone book) they should be able to advise you on your possible stream problem and help come up with some solutions to your problems.