While I am unsure what being a devout heterosexual means you are probably just letting your thoughts wander. However my casual and purely anecdotal observation is that many people seem to change in later life. I am always impressed by stories of married men who in their later life come out as homosexual. Why is that? Is it just because of changes in our bodies chemistry?
Why not just enjoy the thoughts and don't worry about it. I doubt if any fantasy of what it would be like to be with a cross dresser beats what you already have with your wife.
