Friends' Exes

Ok I'd like to hear some opinions on a fight I drunkenly stumbled into with a friend over the weekend because I think she's over-reacting. She's furious with me because she walked in on me hooking up with her ex (they have a house together, that they moved into about 7 months after they broke up which is a whole other catastrophe) despite the following facts:

- I had a thing with him nearly a year before they met

- It happened to come up in a conversation we were having that I would probably have sex with him if the situation presented itself, and she raised no objections

- She made loads of jokes when he and I were both complaining about how long it had been since either of us had sex about how there was one obvious solution to the problem.

So when going on Facebook and complaining about it (which I really don't appreciate because although she didn't name me in it I don't particularly care for being called a whore on Facebook by people I've never met who don't even know all the fucking facts) she was talking about "losing a friend" and shit. Is it just me who thinks that not wanting to be friends with me any more because of this is a huge overreaction?

People kept going on about "breaking the girl code" which doesn't fucking exist where I live, not in the scene we both hang out in. It's a small scene so if we refused to date each other's exes the options are either find someone on-line who lives a long way away or take up celibacy.