PFLAG.org! It was created for parents exactly like you! Keep in mind, it isn’t a “preference”, like if he wants pb&j or mac and cheese for lunch. I will assume you are straight- do you consider your sexual attraction, romantic feelings, and identity preferences? If you think deeply about that, you will get a better understanding of who your son is.
While I know it is hard for you, please always remember that it is 1000x harder for him.
If he is having emotional issues, then counseling is great, but you didn’t mention any problems so don’t think he needs it because he is gay. Would you send your straight kid to counseling if he told you he liked girls? If your kid liked classical music and his friends all liked rap, would you send him to counseling to prepare him for being bullied about that?
Suggest he get involved in a GSA at his school. Or have him start one! Teach him how to ignore the hate and to be proud of who he is.
Most of all LOVE HIM and LISTEN and BE THERE and HUG HIM. That is what he needs from you.