Sex drive?

So I have a fairly high sex drive and I know sometimes people aren't in the mood. However. When my boyfriend and I lived apart, he'd always say how much he was impacted by lack of sex until he could visit me again. Now that we live together, I basically beg for sex almost every night and RARELY get it. Like either once a week or two or even sometimes just once a month. I have severe insecurities and I just need reassurance that it's not something wrong with me... we've talked about it and he says he's just so tired all the time but my mind keeps telling me it's something to do with me. It's my fault.