This is a tough question for a parent to ask, but you state that you want your son to be happy. Here are several considerations: the age and maturity of your son, your relationship with him, and the level of communication you have with him.
Is your son having difficulties in his identity? If so, you may want to focus on this aspect and ask if he would like to speak to someone who is neutral, like a counselor, to help him understand his process of self-discovery.
Education.com has a special section on teenage sexual orientation that may be helpful. (see link)