Betty,
Love your son and listen to your son or you may lose him forever. Telling him his life will be shorter and he is going to hell may not have been the most loving response, but I am sure you were upset. I know you don't want this life for your son and neither would I. He did not choose to have these feelings. He just does.
It will be dificult to find him a good therapist, but if you choose to send him to a Christian therapist be ready for the rebellion. Your son will not like what he has to hear as fundamentalist Christianianity and homosexuality are not compatible. Most ex-gay Christians get that way after years of living and unfulfilled gay life. Is is rare for a gay youth to change, especially with the acceptance that homosexuality gets in some circles.
I do believe that homosexuality is a valid alternative lifestyle, but I am not a Christian, and I would be in quite a struggle if I were. I am also a father and can imagine the heartache and fear you must feel. Be thankful that your son felt he could tell you and start from there. Letting him know you love him and will be there for him are what is most important.