L.A.
Since you are new to the site, we will be treading lightly in answering you.
But if this is a serious question...
If your son is straight or gay, does it really matter?
What is it you really want to know? Probably is he happy? Is he interested in anyone? Is he going to share the information with you?
Figure out what it really is you want to know. Then ask him, but let him know you are aware that he is a private person, but if he ever wants to share with you, you are available.. Also ask him if it is ok for you to inquire in the future.
Our daughter has always been a private person. She is an observer. She takes her time and is very careful about what she shares. So we have always acknowledged this with her, but also told her if she ever wants to share, we promise to keep her confidence if she asks us to.
As our children become adults, we must honor and respect their privacy and wishes. But as parents we never stop worrying. Nothing wrong with communicating this with our children, no matter how old they are.