Am I in the right or wrong?

Girlfriend had a guy friend she's known for a long time that I've never met, over last night drinking and doing blow. i wasn't there or even knew about it until I saw pictures on Facebook that she posted of her and him. I got upset and felt disrespected so I broke up with her. She said I'm insure and that I was wrong for doing so. But I feel this is wrong for anyone to do in a relationship. Thoughts?

Am I in the right or wrong?
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