Boyfriends bday

So My boyfriends bday is coming up and I didn’t realize his date falls as the same as this concert me and my best friend were gonna go to. Keep in mind we just talked about it but didn’t buy any tickets. Now she’s mad at me because I tell her that I’m probably not gonna go because of this bday. He tells me it’s fine to go and that we can do sum another day but I just don’t think it’s right and i don’t want to feel uncomfortable. What do u guys think