What an interesting post. And, an interesting situation too.
Alura had a great suggestion but I think he overlooked where you wrote that you already do compliment your husband often now.
I've known guys that have trouble saying "I love you" and this is probably something similar to that. But those guys don't say it to other women either so it is different.
OK, now this may seem silly but, try both of you writing down one feature about each other that you especially like. Then, when you're both relaxed and have some free time with each other, read what you wrote to each other and talk about that feature and why you like it so much.
Now this might be a physical feature or a personality trait or even a gesture.
Then center your sex with each other for that evening on these two features. For example, if he says your eyes then keep eye contact the whole time your making love.
OK, if it seems to work then do it other evenings too with other features.
This way you and he will find out what features you have that are especially attractive to him. And, he just might be more comfortable pointing them out.
When he meets someone new he sees the features that gets his attention and he comments on them. Maybe he's simply not remembering the features of yours that turned him on to you so much when you first met?
Anyway, it does sound like you have a pretty special relationship other than the one flaw of his.