I'm not going to buy my gf a gift for her birthday
Why wouldn't you buy her a gift?
Because I don't want to do it.
You should at least look to getting her a small gift. When you go to someone birthday you're expected to bring a gift with you.
I'm getting her a gift, just not a big one.
Well I'm glad you're going to get her something at least, I'm sure she'll like it no matter what.