There is much heresy within organized Christianity as in any temporal institution. The Gospels of course warned explicitly about such devil inspired people posing as teachers.
I wouldn’t call him a ‘devil inspired’ teacher....His teachings were solid for the most part. I would call him a teacher who fell into sin of his own design and making ....without question. How and when this first happened I don’t know, but once a sinful habit is establised you will feed it....and he certainly did so as others before him have done.
“Be sure your sin will find you out”