I’m sure it is indeed a shock to the two of you to have your son come out as gay and it is understandable that you would feel upset and at a loss about how to respond. Many parents have been in your position and whether your child is 13 or 30, there are things you need to process emotionally and things you need to consider in responding to him.
Most kids are terrified to come out to their families. Their biggest concerns are parental disapproval, rejection, and that they may be disappointing you. Some kids have even more drastic fears of being disowned or kicked out of their homes. Fortunately, the latter only happens to a small minority of gay children and teens, but it really does happen to some. The tragedy of this is huge, both for the child and for their family. Thankfully, it doesn’t sound like this level of threat is present in your family and that is very good. It makes it a much safer place for your son to discover and share his true self with you.
Young people may know from a very young age, even before puberty, that they are not like their peers. They may find that they are simply not attracted to peers of the other sex and feel much closer to kids of their own sex and gender. While this doesn’t always indicate being gay, it can be so strong and clear to some children that they really do know they are “different” even if they don’t have a word for that difference. Other kids may not recognize their same sex feelings until they come into puberty and find that their sexual feelings don’t mirror the attractions of their heterosexual peers. And some don’t realize their gayness or come to terms with it inside themselves until well into adulthood.
It sounds like your son is one of those who realized his uniqueness at an early age and no doubt it has been a process over time for him to come to terms with being gay. You son is probably quite certain of his feelings or he would not have taken the risk of disclosing this very private information to the two of you. It is also a compliment to the quality of the parent-child relationship that he felt comfortable enough to share this important and still quite stigmatized part of himself with you.
You may wish to seek out some education and emotional support for yourselves to work through your feelings in the wake of his coming out. You will have many more “coming outs” to go through. Coming out is not a one-time thing. There are decisions both you and he will need to make about coming out to other family members and friends. PFLAG (Parents and Friends of Lesbians and Gays) has local and regional chapters and it is worth contacting this organization and attending one or more of their meetings. They are of tremendous help to parents, siblings and friends of gay, lesbian and bisexual youth, providing both information and support to families as well as to the gay family member.
Finding out a child is gay is not the end of the world. However, it can feel like it shakes the foundation of your understanding of your child for a time. Give yourself time to adjust, seek information and support, and keep telling and showing your son that you love him. After all, he is still the same person inside; you have just learned that his sexual and romantic attractions are different than you probably assumed. He is still your son and a loved member of your family.