One of my plates whom I really like also has a friend. Let's call my plate Sierra and my plate's friend Joanna.

So Joanna likes MY friend who we shall call Adrian. Anyway I saw my plate Sierra last weekend, we have also slept together.

This weekend MY friend Adrian is going to see my Sierra's friend Joanna for the 2nd time and hopefully get past 1st base.

When Adrian asked Joanna to come over she said "Me and Sierra wanted to come see you and Fantastico5000 (Me)".

Now normally I wouldn't mind seeing Sierra again but the fact that they assumed I would be available pisses me off. So I want to ditch her for another plate.

How do I get my friend Adrian laid but not have to see my plate Sierra at all?