This could be avocado lacewing. The black fecal matter on the back of the leaves and browning in the center of the leaf are the clues. I just discovered this on my tree today! Apparently it was identified in our area for the first time this past March. Check with your local university extension for preferred treatment in your environment. In the meantime, your tree is small enough that you can clean your leaves by hand. My tree is 25 feet high so I’ll only be able to clean a portion of it. There is a lot of good information on the internet on this pest. BTW, I don’t think your tree is dying. You have some nice healthy leaves.