What you should really be worrying about is whether he is happy or not, rather than snooping into his sexuality, that is for him to discover, figure out, not you; you cannot do that for him, can you?
So relax, and allow him to grow up into a happy young man, gay or straight is actually immaterial in the long run, to him, and to you I am sure!
Parental disapproval is the very reason so many gay teens snap, and go to extreme behaviours, like drugs and alcohol etc. If he is gay by chance, then he would having a tough time, by itself, so your support, unconditional at that, would be a blessing not only for him, but also for you as well, as in his well being ultimately lies yours!
Only thing I would suggest is to come closer to him, by a being non-judgemental presence in his life, and not burdening him with your dreams for him. So that if and when he needs you, you are accessible, and channel of communication are open, and that is best thing parents can do and ask for, from a child this age.
The more you try to hold on to them the further you will push them away! So relax give him space, and love you can, without holding on so tight!