I'm queer and came out as a young teen, so I feel like I can relate to your dss.
I came out to friends at 14 and my parents about 5 months later, right after my 15th birthday. I spent two years being convinced that I could like girls and still not be gay. Even though I was from a liberal family and a liberal community and had no problems with queer people, I was horrified to discover that in myself. I was already a freak at school, I didn't want to be a freak and a queer.
I would have been TERRIFIED if someone had talked to me before I told them. If your dss is indeed gay, he's got something huge to process. This is something that upends your universe. Realizing one's own queerness would be so hard for an adult. As a teen, it's even worse--you're already trying to figure out who you are in the world and what you believe, and you're discovering that you are a person that some people hate just for loving the way you do. I don't say that to make you worry more about him, but only to contextualize the immensity of this process. It's a process you can't rush, either.
I came out to my friends when I was ready, on my own terms. It was an amazing, supportive, validating experience that made me feel so much safer in the world. I came out to my parents when I wasn't ready--they were asking questions about me and another girl (my secret girlfriend) and I felt somehow obligated to come out. I sobbed hysterically for two hours before I could eke out "I'm gay." I wasn't ready and it hurt and I was terrified and it really screwed with my ability to feel safe with my parents, when that was what I needed the most in the world. My point here is that coming out is a huge process--people view coming out as the act of telling other people, but 95% of the process is coming to terms with yourself (or not.) Also, if you call him out about being gay, he may worry that he's in some way obvious in his orientation--that can be pretty scary if you're not ready for the world to know.
He'll tell you when he's ready to talk about it. In the meantime, let him know that you'll be receptive to hear him with love and support when he's ready to come out. Stick a rainbow flag bumper sticker on your car. Talk about your support for gay rights when you read about them in the paper or hear about them on the news. Proclaim your support and love for all people and speak out against the people who do not support and love. Attend a queer play, musical, or community event as a family. Use inclusive language that doesn't presume heterosexuality. All you can do is lay the foundation for him to tell you, but he's got to do the building on his own. I can only imagine how scary that is as a parent, but he might be even more scared than you.
Make sure safer sex materials and education is queer-inclusive. Queer youth are at far greater risk for STIs because we so rarely get decent sex ed. Schools give crappy sex-ed classes as a general rule, but they're very heterocentric. Be the person to fill in that gap.
I'd buy him a copy of Kate Bornstein's book, Hello Cruel World: 101 Alternatives to Suicide for Teens, Freaks and Other Outlaws. (You can find it on Amazon, but this might be a great alternative to find a local queer/feminist bookstore, if there is one.) Kate Bornstein is a nationally renowned speaker and author around queer and transgender issues and is so, so amazing. The book talks in a very accessible way about learning how to love yourself when parts of the world are trying to make you believe you're not lovable. I cried when I read it because I wished so badly that someone had given it to me long, long ago. Even now, long out and a queer activist, that book made me feel much better about my place in the world.
You rock for being a supportive parent. More queer kiddos need parents like you. I can't give you kudos enough for supporting him.
Feel free to PM me if you have questions or want resources. I work in a queer community center, so I can probably find some good local organizations if you're interested.
