I think I am going to spend my money on me instead of my gf for her birthday.
What is the reason why you are going to spend the money on you and not your girlfriend?
I think it's permissible for me to use money on myself. After all, I'm the provider.
While it is nice to spend money on your partner, it is okay to spend money on yourself. After all you have needs that need to be met.
I wish to splurge on myself since I am the provider.
Well, you can splurge on yourself for the rest of the year. I think it would be nice of you to do something for your gf's birthday. It is only one day a year.