Can I tell my attention seeking friend to stop contacting me?
What happened for you to want to cut them off?
I can't stand their attention seeking behavior anymore.
She just really likes your attention, and you should respect that. But if it truly annoys you so much, you do need to cut her off now because she's not going to stop. You've matured, and she hasn't so you can't associate with that.
Maybe you're right. I should stop talking to her.
That's fine, because sometimes we all grow from our friendships and have to move on. You'll both remember your times together fondly, but at a certain point you have to remember that you can always make new friends.