I can't believe I'm in love with my ex wife's cousin
No way. Did your ex-wife find out about your love for her cousin?
No, I can't stand being around my ex-wife.
Before dating an ex's relative, you should have a conversation with your ex to see if they're OK with it. It's important to communicate honestly and openly about it to avoid hurt feelings.
I don't need to tell her. After all it's not like she gives a damn about me.
She may be an ex wife, but don't you think it's more wise to just stay out of her life from now on? How is she going to feel that you are still around, but with her cousin instead? Maybe it's best to find someone else who isn't related to her.