Have a conversation. You love each other, right? Then you should be able to talk about anything, including this.
Gently, nicely, not accusingly, I might add. And also consider at least starting the framing with health concerns. Has he been to a doctor lately? Have you? Then maybe it's time for you both to go, as sometimes losing the sex drive has a medical or a depression underpinning, and if you go to your own doctor, then you won't look like you're just singling him out and blaming him.