Catfish, it sounds to me like some very old hurts got stirred up. By old, I mean from way back in childhood. I have the sense that somewhere in you, RC's reaction to your email correspondence with M felt like a reprimand, which may possibly have spun you into a bit of a tantrum. No one likes being told what to do, or feeling like they've been caught doing something wrong, especially if it doesn't seem fair to us. You did get a tad defensive at first. I'm not saying that you did something wrong or that she did reprimand you, but from your state of mind after that happened, it seems like you have interpreted it that way on an unconscious level. If you think back to when you were young, are there any events or situations that you remember which stirred up similar feelings? Sometimes, just seeing where something came from is enough to diffuse it. If nothing comes to mind, that's okay, too.
I think when you sit down and talk to RC and Charlie, just be truthful and say what you've been feeling and how much you're uncomfortable with these feelings. But I think it will help if you look beyond the current situation, further inward, or at the past, to get some perspective on your responses. Try not to get caught up in the drama and instead, see if you can step back a little and observe your mental process to see what it tells you about yourself. Like a scientist.
Hope that helps!
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein