Bless your heart.
I'm truly sorry for the predicament you're in, BrotherMan.
It seems to me that you absolutely NEED to find someone to talk this situation out with, whether that's your wife a/o F, a marriage or individual counselor, or someone else altogether. But many times troubles grow out of control in the dark and quiet, and die out when given plenty of light and air.
On a side note: it seems to me that your wife opened up the possibility of polyamory in your relationship years ago when she was dating you and the other friend and asked y'all to share her. Having worked then to open your heart to that possibility for her sake, is it all that remarkable that your heart opened itself again? I don't think it is. This may be something you wish to discuss with her/them when the time is right.
I wish for all of you much love, joy and peace. Be strong, BrotherMan.