Inattentiveness issues

Often when my boyfriend starts talking to me (usually this happens in the car) I just don't hear him at all. I don't even realize he is speaking to me until he taps my shoulder or says my name. I am not trying to ignore him, but he says I am ignoring him. I'm not sure what is wrong with me...

Obviously this gets frustrating for him because he ends up having to repeat things a lot. And I understand that. But it hurts sometimes because he gets mad at me for something that I feel like I can't control. I WANT to listen to him, my brain just doesn't register that he's speaking to me until it's too late.

I've talked to him before about this, but he still gets mad, saying he has to repeat himself several times before I listen to him. Once he gets my attention, he just acts irritated and then doesn't tell me what he was trying to say in the first place even when I ask him. This makes me a little upset too (at myself mostly but also at him) because it makes it all feel pointless; neither of us get to talk about what he wanted, I just experience negativity aimed at me and he gets in a bad mood.

I hate this. I don't know what's wrong with me or how to make it better.