You are way overcooking your meat. I know some people want to overcook chicken meat for safety reasons, but here's two ways I cook chicken breast for very juicy meat:
Step 1: right when you buy your chicken breast, before putting them into your refrigerator, salt them! Salting them way before will make them much juicier later.
Step 2: a while before cooking, take the meat out of the refrigerator to adjust to room temperature.
Step 3: This depends on whether you want to cook it in fat, or in water.
Method 1: Cut the chicken breast however you want (or don't cut it), and cook it on good heat but not so hot that your butter burns. From time to time check the inside of the meat to see the color. It will cook from the outside in. Stop cooking before the meat is bright white. Now let the meat rest for a few minutes, and check the inside of the meat again to see if it's cooked. Don't expect it to look stark white and dry inside, because guess what, then it will also taste white and dry. It should have a soft white color, and be moist inside. The cooking time will depend on how big your pieces are. If you cut the breast into about 10 pieces, then this may take only 3 minutes to cook. If you've used the breast whole, it will take longer and you'll have to use lower heat not to burn the butter. After you've cooked them in this way for a few times, you get a feeling for it. Serve the remaining butter as a sauce, and make sure to get all the browned bits in the pan, they have the best taste. Or use the remaining butter as a basis for a sauce.
Method 2: If you want to cook chicken by boiling it, don't boil it in boiling water for several minutes. It will taste totally dry. For example for a thai chicken soup, I bring the soup to a boil, then turn off the heat, and then add the uncooked chicken pieces. The remaining heat of the soup is more than enough to cook the meat well if the pieces are thin, but it will not overcook (always check for doneness before serving of course).
The salting and bringing the meat up to room temperature helps, but if you overcook the meat later, it's all for nothing. The key is to not be afraid to undercook it. Better undercook than overcook, because if you undercook you can always cook it a little extra, but if you overcook it's impossible to undo it. If you've never tasted perfectly cooked chicken breast, then perfectly cooked chicken breast is going to look and feel undercooked to you, but as long as the meat inside does not look raw, you're good.
You can also consider switching to chicken thighs. You can cook those way longer and they'll still taste good. Though I would not recommend cooking them in water, because they'll be tasteless. By far the most tasteful basic way to cook chicken is just with salt and butter.