I'm going to take my ex's cousin on a trip with me
why do you wanna take your ex's cousin on a trip?
Her boyfriend dumped her, I want to take advantage of her situation.
You should not interfere with your ex's life. Let her be and you move on with your life. If you hang out with your ex's cousin it'll make things complicated.
I want to help my ex's cousin out and she'll be mad at me if I don't invite her to my trip.
It doesn't matter if how she will react. You should stay out of your ex's life and leave her family alone. Find someone else and move on.