Am I overreacting or is my bf an asss

It’s my bf birthday and he was venting to me about how much his family sucks cause they don’t plan anything for his birthday cause they think birthdays are only for little kids so I offered and said let’s me and you do something for your birthday let’s go out to eat and he said okay. Then 30 minutes later he calls me to tell me his older brother just called and invited him over his house to order him some pizza so they can hangout for his birthday. Me and him already had plans. That kind of stung my heart. He then said we can do something later on after that like at 8:30. He knows I have a curfew. Am I overreacting for wanting to do something with him on his birthday I feel as if he chose his brother over me or just threw out plans to the curb. Then to add to it he told me his dad told him that I just wanted to celebrate today with him cause I wanted a free dinner date when in reality I was gonna take my bf out and my bf knew that. Am I overreacting or is my bf being an asss? I feel like he could’ve easily told his brother he was gonna go out to eat with me but could go to his house after our date.