My partner has a low sex drive...I need imput

We've been together for a little over a year and a half now. At first we had sex a few times a week, which I thought was normal. After a while it dwindled to around once a week, which I was fine with and kind of suspected after the "honeymoon phase" of our relationship. But now we haven't had sex in months and I'm starting to wonder what to do. He has even brought up that he doesn't know what happened to his libido and has apologized. I tried to comfort him thinking maybe it was stress or something mental, but it has not solved anything. I really don't know what to do at this point. I know it's normal for people in a couple to have different sex drives but this is too long for me. I'm starting to feel disconnected from him and and kind of feel like we are just going through the motions. I mean what is a relationship without sex!? I just don't know how normal this is, or what to do.