Should I spend money on myself?
I don't understand. What exactly do you mean when your saying that you want to spend it on yourself?
Spend it on myself rather than on her.
Its only natural to want to spend your money on yourself rather than someone else. It takes a special person in your life for you to want to put their needs above yours consistently.
I really want to show my girlfriend that I just want her to be happy. Is it ok to treat myself still?
Well you will have a hard time convincing her of that but it is still okay to treat yourself sometime. It is important to care of yourself before you take care of others.