My friend is making me resent her?HELP!?

I dont know what to do anymore. I've been friends with her for a long time but as soon as she got a boyfriend she was different. ITS BEEN ALMOST A YEAR! and she'll put he's feelings before mine and really seems like she doesn't care. After an argument about it she said "she's going to do what she wants to do". what does this even mean? it seemed like things were going all right until a couple days ago i asked her if she would take my babysitting job because i had college orientation and my brother who had surgery had to go to the hospital. After being a little rude about it she said yes. then the day right before she cancelled on me and it pissed me off. Her excuse was a silly one too. My question is should i even bother my self with her anymore? And am i right to be mad? please give me some advice.