Did you consider him a Catholic? Do you realize there are many other priests you have met who helped you who you now, maybe without realizing it, aren't Catholics. Ask yourself, did you think they were illuminated by the Holy Ghost? And if so how could that be if they adhered to heresy and blasphemy. It's easy to point at a Pope, but we have to remember that almost all Catholics who are traditional, let alone sedevacantists, have had some contact with a good priest who was not a sedevacantist and it's clear they have the gifts of the Holy Ghost.
I feel horrible too and yes we should pray for him.