Hi there, and what an excellent post.
Don't be hard on yourself, we were all fooled, but, I think that says more about our 'goodness' as people,
which is something everyone should be proud of.
It has to be our own mind, that does the work. We have to do the work to feed the mind, which controls everything else, I believe.
Someone can tell us something until they are blue in the face, but until we 'get it' until it clicks in us,
We just won't get it. and everyone's story and experience and how it has affected them is different. there is so much going on under the water with each person, it's a long process.
It may not just be the 'truth' with him, there could be many underlying issues that have been festering within since childhood, family issues, lack of love, abuse, frustration with the world etc ( our 'breeding' what's in our blood, temperament, fiery person, calm person, form of autism, etc, the list goes on) I am a naturally fiery person, it's in the blood.
He has to get to the root of it, and find out why, and what is causing the anger and bitterness, sometimes we don't even know or realise we are angry and bitter.
Being able to talk and express everything is vital, which is why therapy is so could, therapy is not just visiting a trained professional, it could be as simple as talking with the right person, support group etc. the more he talks, the more he will think, feel, reason, question, search, it's a process of healing.
If he still believes in God, explain to him that he is putting a barrier between the to, the more he researchs and learns this, the easier it will get.
I found two simple books excellent.
Teach yourself Psychology
Teach yourself Cognitive Behavioural Therapy.
I have learned so much from this site, and from the many excellent posters. jgnat in particular, she has great qualities.
If he could start visiting and talking and thinking, I think it will get him on the right 'path'.
Great to see you care enough to try to help him.