I think you're right on all counts. I don't actually want to stop my colleagues from working on this idea. I am happy that someone is working on it and, though I still have some ideas in a similar space I would like to tackle, I'm not expecting them to let me work with them (nor do I want to). I don't care for equity as, like you said, the idea is worth nothing.

I am hurt on principle as it feels like a violation of a professional and personal relationship built on trust and loyalty. I was first told over an IM program and I did not want to make the accusation of impropriety over the internet. I would much rather meet and discuss in person (I am not a fan of difficult conversations asynchronously). I think you are right that the only option forward is to address the situation because I am not the type to let something like this go. But, I wonder if I am bullheaded and should just cut the losses and accept it. The odds are this idea does not work out for these two and the practical reality is that they move on to something else. It still feels bad.