It sounds like you want to do the right thing but are scared of losing both of them. You could always decide not to pursue it with your other lady and just leave things the way they are.
THEN you can tell your wife your decision: "Hon, there's someone I care deeply for but you mean so much and I would never want to jeopardize what we have. But because you are my wife and I respect you as an individual, I must tell you this because I think you might have an idea already and I would never want you to think I was cheating on you."
Something along those lines. That way, you have opened a dialogue yet established from the beginning that you value your relationship with your wife.
I just came right out and told my husband that I fell in love with this guy I knew from 20 years ago... He wasn't surprised or alarmed, since he heard me talking on the phone for a week... it was the other guy who freaked out when he learned that Husband was ok with it.