<human>: Can you condense the text into a few key points?

Ok so a little background story, I was with her for 6 years. I kinda found out she wasn't as loyal as I thought she was and pretty much cheated on me emotionally recently this year and broke up with me for that guy. I took it hard of course but after finding out how she went behind my back and the things she did that I never knew of, I don't want to have or see this person in my life at all.
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Ok so technically we've been broken up for about 8 months, only actually been physically apart for 4 months. Here's what I need advice on, I don't want to see her, I blocked her from everything imaginable, I don't want to run into her, but my friend's birthday is coming up and he's having a get together. She was invited, now I don't know if it was just because or they actually want her there.. Not that it matters. But now I don't want to go anymore because I do not want to see her at all. But at the same time I do want to go for my friend. It seems like a lose-lose situation, if I don't go she might think things, if I do go then I will see her and run into her. Awkward. 

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Now I pretty much let my friend know before that it's either me or her, he doesn't really care for her either because she's not that great of a person. But his gf invited her, probably because they still do talk here and there. She knows about my situation also and knows what I don't want. So I hate to make them choose but I just feel like in this situation they will have to. I rather not hang out with anyone than to see her again, as much as I'm over her, I still very much dislike what she put me through. Stringing me along, dragging me, not making up her mind and in the end dropping me like nothing. Over the years apparently this isn't the first time she's done things behind my back. If she does that I can't imagine the things she even thinks of doing.
<bot>: My ex of 6 years is possibly going to my friend's birthday gathering, I don't want to go anymore because of her. What should I do?