Aaaawwww, happy birthday!

The worst is managing your own emotions when someone you love disappoints you and doesn't live up to your expectations.

I hope you can find a way to turn around the remainder of the day even if it's doing something that is different than your original expectations.

Maybe talk to your boyfriend and express how upset and disappointed you are, and ask him if he realized what this day meant to you, and see if you can augment your understanding of the situation with his perspective as well.

Maybe you can also plan to have some things for the discussion that could be done to salvage the day or that he could do to make it up to you another day.