How well does he know his father/stepfather? Do they get along well? Sometimes, prolonging a good relationship (and revealing sexuality later), can do more damage. just imagine, if they have a great relationship, your son may be completely devastated by his father/stepfather's reaction.

If they don't get along well, it may be easier (but will more likely than not, still be painful)

Chose a good time, plan carefully, but first off, let your son explore his sexuality! (He's still growing up, and has a lot of hormones, he may just be confused!)

In the event that he does identify as gay, make sure you treat him as you did before. He doesn't want pity, he wants to be accepted, but most importantly, he wants you to be his mom! He needs you.

If all else fails, just be there for him. Remember, he comes first (especially before an ignorant husband.)

Take care!