What does Heather do as a final blow to Melinda?

Heather dumps Melinda as a friend..... she completely devastates her.

Heather: [smiling with her mouth but not her eyes] "We were never really, really friends, were we? I mean, it's not like I ever
slept over at your house or anything. We like to do different things. I have my modeling, and I like to shop ..."
Me: "I like to shop."
Heather: "You don't like anything. You are the most depressed person I've ever met, and excuse me for saying this, but you
are no fun to be around and I think you need professional help."
Up until this very instant, I had never seriously thought of Heather as my one true friend in the world.

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Heather: "Look, you can't eat lunch with me anymore. I'm sorry. Oh, and don't eat those potato chips. They'll make you
break out."
She neatly wraps her trash into a wax-paper ball and deposits it in the garbage can. Then she walks to the Martha table. Her friends scootch down to make room for her. They swallow her whole and she never looks back at me. Not once.