Should i be mad?

so I really like this guy I go to school with and today my friend was walking with him and I came to talk to them and she looked at me weird and they left me?!? Then at lunch i went to sit down next to him and she sat down right in front of me?!? I don't know what to do I don't want to start anything but she knows how much I like him and she just got out of a 8 month relationship so I'm not sure what to do?! Advice please