Everyone's libido is different, and everyone's levels of hormones are different, and this is clearly the case with you and your boyfriend. For some people, an average of twice a week is perfect. For others, it isn't. It doesn't mean there's anything wrong with either of you!!
Have the two of you been able to talk about this? If so, what was his response? I know it's a sensitive issue, but it's clearly important to you. Unless he is depressed (which can have a serious effect on sexual desire), this is just probably his normal level of hormones and desire.
And how different are your desires? If it were up to you, how often would you have sex?