I'm hurt and don't know what to do

I need some friend advice. Me and my friend, Jessica, have been best friends since kindergarten. This year, things have been almost the same, except for Marie. Jessica is dating Marie's cousin. They have always been friends, playing volleyball and doing track together. Ever since Jess started dating Marie's cousin, the have been getting closer. No problem, i like Marie. Well, me and Jessica had plans for today. A few days ago, something supposedly came up and she cancelled. I was fine with it and we moved on. Fast forward four hours ago, i get a text from a good friend on a date with boyfriend. She knows about our cancelled plans and sees Jessica. With Marie, bowling. I am extremely hurt over this. I don't remember doing anything wrong to upset her. I feel like i'm being shoved out of her life and replaced for no reason. I have spent the last hour crying (totally out of my character) and avoiding everyone. I understand things like this happen, but why without reason? I have friends besides her, but not as close. I just don't know what to do and am stressing myself out. Please ladies, any help?