How I Felt When I was Lied too.

Recently I have been lied too from someone whom I believed was a friend. Long story short she thought someone from my past who hurt me was more important than a project at school we had that day. For the past while I have had my friends straightened out. I know who to trust who not to tell secrets too and who will always have my back no matter the circumstances. So when I found out that this certain someone bailed on me basically making me look irresponsible to my teacher and still felt healthy enough to go out that night I was very angry. She was sneaking around and there is nothing that i hate more. I am a very upfront person and its one of the most stressful things for me to have someone you think you can trust break that trust. Currently I am trying to just put it behind me , her loss right? But it's not that easy I am still really upset and less angry but still shocked that she would do something like that. I'm trying to be the bigger person and be gracious and not make a big deal out of anything but the feeling of being back stabbed is still there.