>> What should I say to her when she brings him up? I've been bringing up my ex everytime she mentions him.>>
I'm guessing her ex dumped her, despite what she says, because that's the way it goes: whoever gets dumped is the one that feels the pain. And she's newly dumped and going through the process of being hurt and she vents to you because she doesn't have anyone else to vent to, and women HAVE to vent.
One thing I would NOT do is talk about MY ex to her.
>> just recently she mentioned it was both her fault and his. And that's what has put up a red flag. >>
I don't see it as a flag. I see that as her being diplomatic. Imagine if she was cussing him out and laying ALL the blame at his feet. You'd have to think "what part did this chick play in it? She wants me to think she's a saint?" Better that she's diplomatic.
>> I'm here for you if you need to get this stuff out but I'm not gonna sit here and be your emotional sponge if you are having second thoughts." I'm a brutally honest person >>
Here's a tip for you: "brutally honest" is another way of saying "I'm tactless". Tactless is going to turn people off while you go around claiming that you're just being honest. Instead of using the crass "hey I'm not your emotional sponge" line, which is kinda hard, try handling it this way. For five minutes you nod you head understandingly and make empathic sounds like, "uh huh" and "oh" and "that must suck". Then you bolt up and enthusiastically state, "Hey! Let's get going! I don't wanna miss the [insert whatever your plans are for the night here]!"
She'll feel "heard and understood" which is all she really wants, and you're not being an emotional sponge. You just helped her vent and feel better for a few minutes, that's all, and now it's time for the real reason you're there: FUN. THAT'S what you need to remind her of. The positive (Let's go and have fun) she'll associate with you, not the negative (I am not your emotional sponge).
The deal is: she's hurting but we don't know for how long, so don't make it worse. Maybe she'll forget all about him by next week if you two have some fun times.