Well, I’m sorry first off. I can say a few things about it but I’m not sure I will have the answer since I don’t know him and you.
First, several things like weight and age are a factor, which contribute to lower testosterone sometimes. So there may be a biological component.
Second and more important, it sounds like you have a communication disconnect. If you have expressed this and he doesn’t “understand”, then you need to make him understand. I understand and you hardly told me anything so he definitely should be capable of understanding.
Now if “he doesn’t care”, then you have a bigger issue. He should give a shit about his girl’s emotional state or else maybe he needs a wake up call.