First, welcome and thanks for asking the question! It sounds as though you have a very special marriage to survive this journey you have both made. God bless! And you sound like a very special wife to be so supportive and to even consider RCIA. God bless! While I agree with the ideas already mentioned regarding finding some form of common prayer and devotion, I wanted to add something else that follows up on another posters comment.
While I know many non Christian, mixed faith marriages survive and succeed, coming from a mixed faith , Catholic and Protestant marriage, I know from experience there are distinctions that can cause issues. These issues can be worked around but even with the most cooperative couples there is still the absence of the bond of having a shared faith life. This is not to say there are problems per se, but rather there is an absence of a more ideal harmony. Of course, discord can occur in a marriage of two Catholic spouses when one is very devout and the other is more liberal and rebellious. In fact this can perhaps cause more problems because there are expectation of harmony in a shared faith. But the point is that when a couple have a shared faith, a faith in which they actually hold in common all the beliefs and practices, there is a unity of the marriage that I did not experience, but that I know does exist between Catholic couples, that I believe is the ideal. Marriage is hard enough. I think the bible’s call for a marriage that is “equally yoked” is not just a good idea but the ideal.
So, as a Catholic, I naturally would feel that the ideal is that you would be Catholic and share the faith in the same manner as your husband. It seems he is being understanding in your decision not to become Catholic and I pray he will continue to be patient and respectful of your decision so that you marriage will continue to succeed. However, I would also like to follow up on a point of a previous poster. What exactly do you “protest” in your Protestantism? I would simply suggest that while you gave RCIA a shot, you do not close the door on the Church. While you were not convinced enough to leave your tradition, I would suggest that in your seeking truth you remember that there is only one truth. Christ either left His authority to One , Catholic and Holy Church or He did not. The Catholic Church claims its authority from the Apostles as Christ handed authority to them. This authority includes the creation of the canon of the bible and the Church’s authority to interpret the bible. As an Evangelical, who is the ultimate arbiter of truth in your interpretation of the bible and hence your beliefs? Yes, the Holy Spirit guides us to truth. But there cant be thousands of versions of truth as each Protestant denomination proclaims. Perhaps your one church hold the absolute truth out of all other denominations. But on what basis can you claim that? Does your particular church actually teach New Testament theology? If that were the case it would look like what the Church Fathers taught. But the Church Fathers , even the ones of the second Century , those taught by the Apostles themselves, were Catholic. They believed in the real presence of Christ, the primacy of the Chair of St Peter, the sacramental nature of the Church etc.
In any event, my point was not apologetic. It was that my suggestion to your situation is that one cannot go through RCIA , read even a great number of books and suggest the search is over. And that if you were my wife, I would be perfectly elated if you simply told me that while you choose not to enter the Church at this point, you would continue to be open to the truth , to what the Early Church Fathers taught, what the Catholic Church teaches. As a Catholic, one must be open to truth. For me that means that I learn from the Protestant world, through Christian radio and TV. I ponder the issues and raise the questions. I stay open. I happen to be confirmed in my Catholic faith, but I remain open to truth. My suggestion is that you simply remain open . Learn what the people closest to the Christ and His Apostles had to teach. As a good Evangelical, you are called to understand the bible. How better to learn what the bible teaches than to study those closest to it, the Church Fathers.
Of course what is good for the goose is good for he gander, so if you are willing to continue to learn, he should also be open to hearing good Evangelical teaching. My Catholic faith has been strengthened by good Evangelicals, but it has also been weighed against my Catholic teaching, which is how he needs to approach it.
So that is my suggestion to your situation. God bless you and your husband and your very special marriage!