So my girlfriend went to work even though it's my birthday.
Was there something wrong with her working?
It's my birthday! You can alway go to work.
Even though it is understandable to be upset that somebody can't go with you, people need to keep their work commitments. Otherwise they could get fired.
It's inconvenient to me and she doesn't give a flying fuck even though it's my birthday.
Even though you want to go out on your birthday there could have been an emergency at work or something.