Dear Jayne,
I can understand you feel anger inside of you. I think particularly since he is continuesly lying to you. Its good that you try to keep speaking with each other and this for sure should be the key factor of success. What your man is doing does not sounds strange to me. I had a lot of secrets about my sexual fantasies to my girlfriend before (10 year relationship), part of it even was about homosexuality. She did know only top of the iceberg so to speak. I didn't like to hide it but for some reason we couldn't talk about it. Our sex-life was ok (or at least I thought at that moment), but I was missing something (I have a strong sex-apetite and fantasy). In the end we broke up (my decission) and a part of it had to do with this. I promised myself that if I step into a relationship ever again then big secrets should be discussable. And there she was, the lady that was so enthousiastic about everything including sex that there was nothing to hide, everytime there is something we really talk and try to make our fanatasies work. As a result my secrets are 100% history although still I masturbate and watch porn with it, but she knows and think it's ok.
What is the connection with your husband, I don't know. But some simularities stroke me; First of all I had a lot of fantasies about homosexuality...now since everything is open and we can discuss everything its gone, strange but true. Your mans fantasy about a different type of female might be part of his FANTASY world and has nothing to do with his affection to you. All in all if our fantasy world wa 100% like our normal world, why we still need a fantasy world. In Dutch we have an expression which state: "The grass at the neighbours garden is always greener"
Secondly; my ex-girlfriend was only interested in WHAT I did and hide for her. Never was she interested in WHY I did it. This might be the reason why you still find out about your husband actions. It will take a long time and even more trust from both sides to really understand WHY he has these fantasees and why he is doing it. By really be open there is a good change that you will find a solution.
Males fantasy is partly different from females and much more conected to action. But I found out that if two parties are open (male and female) and willing to really listening to each others interests you could both gain. If you just see his actions as treath (and he sees it the same way) then he will be just defensive (and you as well) and each of you will never understand each other.
I'm not sure if this was helpfull for you, but it might gave some background in the males world.
All the best!
Barry