“Obviously I can’t tell him or anyone” is as good as showing an apple without all the worms inside. As hard as it may sound to swallow this (inner me: seems like you have no issues with that considering your polygamy), you have to hold yourself accountable. If you cannot stay true to yourself, you will torment yourself more with it. You can either come clean and stop wasting both your and his time (chances are they will find out - it’s his best friend, after all) or you can continue living in a lie, one that will hit harder as time goes by. It is completely right to feel guilty, meaning you still have your morals in check.
On another note, great nickname pick. It expressed exactly my emotions as I was reading. Went from “I appreciate her expressiveness” to (censored due to vulgar language).