Is it normal that i'm angry?

It's my boyfriends birthday. We live two hours away from our parents (different cities) and most of our friends. Al though we see them every other weekend. I go to school and I work part time as a waitress. I'm not that financially well off and my boyfriend knows this, but I offered to treat him to dinner for his birthday. We went to a fancy restaurant(literally costing me a weeks worth of pay) which I had no problem with. About half an hour after dinner he got a text from his friends wanting to take him out for some drinks, when he had already promised the night to me. He's also going out to his parents house tomorrow to celebrate his birthday with them and all of those friends that wanted to take him out tonight and leaving me at home to work all weekend. He met up with his friends at the mall beside the restaurant we had dinner at and had me drive myself home. I know it's his birthday, but was it wrong of him? Or am I just being selfish.