(If he was your son, swooning over the 11 yr old girl next door, I doubt you’d question either his sexual self determination, or his age worthiness to know his own mind!)
Your real issue is that he has taken full ownership of his sexuality at twelve.
And he unequivocally has, whether you’re ready or not, I’m afraid. Understand, I’m not saying you’re wrong, it is entirely possibly he’s just going through something and it will shift again. You should look really hard at why you choose to believe that, and how much asking him to be discreet is about you and not him. I should think any parent might easily be blinded by what’s really driving what they feel in their gut. It takes a lot of self awareness, in fact, to even consider that perhaps your view is not so clear as you believe. I mean, does he seem unready? Or is it you that’s unready?
But regardless, I’m afraid the really hard truth is you cannot take back his ownership of his sexuality from him. All efforts in that direction seem to me, destined to failure and run the risk of solidifying, via defiant reaction, the very lifestyle you’re hoping he doesn’t ‘choose’. (Whether you can see that, or not.) I realize that’s a lot to unpack, but you’re going to have to up YOUR game in the calm and withdrawn department I suspect.
You said you supported him. I believe you meant that from your heart. Now comes the hard part. You’re either going to live that as true, or demonstrate how it’s actually not. I know your fear is he must face a harsh world, and, again, you’re not wrong. But he seems to be facing his part of this struggle/journey head on. He seems to know where he’s headed. Any attempt to diminish that is gonna break his heart.
He seems up for whatever lies ahead on the journey he’s on. You need to be doing some rapid catching up, I’m afraid. Because you seem to want to start the journey you’ve chosen, ('We support you!"), by trying to slam on the breaks, keep things hush-hush, and discrediting his authority.
It turns out he needs your support NOW. Right now. Not when you’re more comfortable. Have had time to process. Have doubled checked its real. Waited till he’s older.
I fully believe your moment is RIGHT NOW! Choose your course carefully. Wishing your entire family Good Luck.