As per normal, everything I am about to say could be completely irrelevant to your situation. It is from my perspective
I'd say you are up against one of the hardest things for a person who is monogamous to understand; that the words you say to him are the same you say to another and still have any meaning. The other thing is the concept of value where there is quantity. Let me explain a little and I hope this helps. A coin or comic collector generally appreciates and has faith in the value of a rare edition to his collection. They treat it different, show it off, pamper it and feel a certain pride that they are the only one to have it. If they were to suddenly discover that almost all other collectors had the same edition or could acquire it, its value plummets in their mind. There is nothing special or unique about what they have anymore. So now the challenge for the collector is to find value from a different perspective, based on different criteria or discard the idea that the coin/comic is a valuable commodity.
The duplicity of words spoken to lovers is a sensitive topic. I sometimes get hit by the transference of experience when Redpepper and I are together. We could be doing something and I will switch into a space where it is someone else with her...not her husband, but maybe her tertiary or non sexual boyfriend, or maybe just a friend. She is responding the same way, saying the same things, looking at them the same way. It's not particularly pleasant and this type of thing might be what your husband experiences. So while you're on your knees in front of him (using your own words merely as an example) he may be seeing you with others in the same way.
He needs to find his own faith in what you say to him. I think you've done your part, now it's up to him.