Is telling a grl my cuzin told me ur family is a slut wrong plz answer?

Cuz I told this to the grl I like becuz my cuzin was tryin to steal her from me than this caused a big problem. It's long story but now she mad at me becuz she thinks I'm lieing and won't talk to me anymore. I had to say that to her I had no choice she wouldn't stop talkin to my cuzin. We went out twice and it pains me that she won't talk to me again plz help