So, how about you say something like, "I can't promise I will never want that with someone. I CAN tell you that in 19 years I have never been physically intimate with anyone but you, dear wife." and you can promise that you won't unless you tell her.
Because it could happen that someday you will be able to stand the thought of losing her.
Perhaps NOW is not the time for promising things that can't be promised. Maybe you can ask her to be yours for a year, while you both let raw emotions process and settle and gain more information. And that you won't even look for a romantic friendship for a year, until you've both had time to deal with living with this brand new knowledge.
Just a thought. You've known who you are, and struggled with it, for years. She just found out. A week or so ago.
Love is that condition in which the happiness of another person is essential to your own...
Robert A. Heinlein
Me: female, bi, (formerly hinge of a vee)
with FirstBoyFriend (FBF)(moderately long-distance)
and no longer with CurrentBoyFriend (CBF)(who lives in the apartment building next door)