I take it that your ex-gf is talking "smack" about you, which is what hurts? Did you two break up on decent terms or was it a hurtful break-up to begin with?

You could try contacting her, and being honest about how you're feeling. Of course, that's risky. She may not be real sympathetic towards your perspective. Is there a way to smooth things over between you and her, yet still keep your emotional/sexual space between one another? Or is it "all or nothing"?

I hope that you're able to get this mis-communication resolved soon. Best wishes to you!