On the inside of my shoes I often get this issue:
Can i fix it without going to a shoe repair? would it be expensive to fix and how to avoid it in the future? It happens to all my shoes...
I have that problem too, here is how I fix it:
I obtain a small piece of leather that is smooth on one side and rough on the other. I cut it to cover the damaged zone plus some overlap. I then use contact glue on the rough side to glue this patch into the shoe (following the directions on the glue tube).
You can get small scraps of leather for this purpose inexpensively at an upholstery shop that repairs chairs and car seats using leather.
In this way I have been able to get many years of use out of a shoe where the leather in the heel has started to break as in your case.