Re: slowly killing my banana tree :(
It appears to be water stress to me. I've seen it when rainfall is not ample in a large orchard. Bananas like to be no drier than MOIST. They prefer WET but not to the point where their roots are standing in water. If the soil around the corm gets dryer than moist, the plant will suffer and the usual symptom is yellowing along the leaf edges that turns to complete necrosis.
Hope this helps.
Aloha from Hawai'i