Sex drive

Hi guys! I've been kind of bothered recently because it's happening more and more often that my boyfriend wants to have sex but I'm almost never in the mood for it. It's not that I don't find him attractive. I do and I love him. He says it's fine that I say no and that he would rather not than me saying yes for him and not myself. But he still gets bummed or sexually frustrated because he's in the mood and hard but he can't do anything. I'm concerned about how low my sex drive seems to be compared to him. Any advice or insite?