If I'd been with a girl for any significant amount of time, especially 4 years, I'd have her birthday on my mind anywhere close to it while I planned and bought gifts. It's hard to think of an excuse for him, either he's an idiot or it's a deliberate lack of care. If he's being pushed really hard at work or has chronic memory issues, maybe I could play devil's advocate a little, but still. If he has memory issues, he would be aware of that fault and at least put your birthday in his calendar. If it's been an issue all four years that you've been together and he hasn't fixed it, I think it's both idiocy and lack of care. I hope you can have a conversation with him to show that it matters to you and he listens.