Wow, I'm so sorry you're going through this. What a huge turn around in your marriage. I feel for you.
I agree that your husband may have some things to work on. Poor guy to be struggling so much. Sometimes in relationships people get so entwined with their partners that they covet them and keep them in their heart as if they have ownership over them. Of course they don't, because their partner is a person who has freedoms and desires and a life of their own. Yet it can happen without a couple knowing it is. Perhaps he and you are co-dependant?
Sometimes when a couple are doing the same thing for years and one does something different for a change, the whole boat gets rocked. It looks like your boat is rocked by this situation.
I think its a great idea to end this relationship you have with this guy to focus on your marriage. However, I also suggest that you don't lie. You could use this opportunity to make some changes in your marriage for the better rather than go underground. Going underground for the sake of someone else leads to depression, resentment, and the distruction of relationships in my opinion. Better to figure out what you need, ask him what he needs and go from there. This might require a therapist to help you as its no easy task, but I would like to suggest that if you are able to reach a point where you can negotiate some boundaries around your needs and then stick to them, you will have a better marriage and life all around.
I would wonder if one of your needs isn't so much to be with this other man, but to have the opportunity for closeness with another man in general. Or people for that matter. What are you doing I your life that is just for you? What kind of things can you do with your husband that are different? These may be the questions to ask. I think with time he will get through his inability to have sex. Sure its alarming but it is sending a message that has another meaning. What is it? Better to figure it out while the emotions are still fresh.
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