i came out the same way to my parents. the first thing, iwas only 13. they said not to brand myself, but to keep myself open to anything, any changes, any feelings. afterall, i was just a kid.
you must accept him. after a while you can bring up how he wont be saved if he remains gay. but HELLO, first hes just a kid. so please, give him all the support he needs, give him help in school and in life all around. when he reaches 20 or 25, then you can try the idea of changing. who knows, he may not be gay at all!
love. right now thats what he needs. not how you think gays are condemned to hell, personally, that does not help.
you as a mother must show her love. as a christian, you can do ur duty of converting once hes reached the proper *mature* age.