Never mind the coming out to the friend, what is this "I'm being forced to break contact with her" stuff? Is there some aspect you didn't mention? While I think it is somewhat improper to tell the friend before the SO, Her telling you to break off a friendship? Uh uh, not acceptable. If she has some reason to doubt your fidelity, that's one thing, if she doubts it without reason or evidence that's something you two have to discuss, but just break it off because of what might happen? Are you two married? If not, I'd be telling her no, deal with it, or leave.
Of course if there is something else you forgot to mention? Or have I got hold of the wrong end of the stick?