I want to preface my remarks by saying that I applaud you for preparing to talk with your husband. It's difficult and I respect the bravery that you must find in order to do so. I think you will find that your complete honesty will be such a relief to you, even if the consequences may be difficult.
Just because he hasn't asked and doesn't seem to want to know doesn't mean he doesn't need to know. The difference is very important, especially if you are hiding something hurtful from him. Besides, the fact that you believe that your husband would be unhappy if he knew about your actions is the real indication that you're not being truthful and honest with him.
I wish you a lot of luck.