>>41218236Have you tried taking a peek into his mind to see what he likes? It sounds like he gets off on you not knowing, probably rooted in him thinking you'll push him away.
If you're cool with it, you could either come clean about knowing and try to work something out. Or you could tease him with it, and pretend to wake up during to put him on the spot. He might like that, depending on how he is.
Either way, you could help him stop doing it in secret and let him do it with you. You could help him get it under control.