You already know the detailed diagnosis, which surely must have been told to you by a proper qualified person (a doctor)!
Here goes my assessment and suggestion:
You seem to be suffering from a chronic anal fissure
. Any form of conservative (i.e. non-surgical) treatment is unlikely to work at this stage; and I am sure you must have tried all sorts of them by now.
At this stage, surgery seems to be the only option left for you. Lateral internal sphincterotomy (the name of the surgical procedure) is a 'minor' operation (even if the name is slightly lengthy!) with ~ 95% of success rate. The sentinel pile can also be excised easily at the same time.