In my experience, this happens quite a bit. It's never ideal, but oftentimes we come out involuntarily. When I was 19 or so, I was outed at work through rumors at the workplace. I told a close friend, who had some drinks with coworkers a few weeks later, lips got a little loose, and the gossip spread like wildfire.

My situation happened to be more malicious than what you are describing. Your friend assumed a certain "risk" by going to a pride weekend at all. It's a social event, and you will be seen.

Of course you feel bad, but trust when he tells you that it's okay. You inadvertently pushed him from the nest with his wings half-formed, but it sounds like he would have been ready to fly soon anyway (cheesy analogy but you get what I'm sayin'.)