In some cases, those feelings just wont go away. No matter how long you try to deny them or how much you want them to. Believe me. They tortured me for three years and guess where I ended up.
It is a bit of a sticky situation, but the way I see it you have two options. Keep going along trying to ignore your love for F, which doesn't seem to be working out too well for you, or talk to your wife about it again. Make sure she understands just how much you love and adore her, and that your loving F doesn't take away from that at all. Approach the subject calmly and hopefully she'll listen and take it in and consider it.
Does F want to have a relationship with you? Or is she just flirting? This would be something to defenately make sure of before speaking with your wife if you're that worried about it.
Unfortunately you seem to be stuck between a rock and a hard place. I think either you'll need to risk the conversation with your wife or keep being miserable denying your feelings.
I wish you well and hope it works out for you.
"Thou art to me a delicious torment." - Ralph Waldo Emerson