That's difficult. I was married to someone who was almost the same way. Could never express what made her happy, or turned her on. We ended up splitting up.
I don't wish that on you, or am saying what i did was right.
I say keep trying your best to get him to engage, and talk to you about what it is he likes, and dislikes.
Maybe if you let him know what turns you on, he may share a little more, albeit slowly. π€