Thank you for your insightful reply!
I did mention polyamory to my wife, and I did tell her that I want to be with both she and R. That is definitely an idea she is uncomfortable with. I shall attempt to sit down with her and have a full discussion dedicated to the issue of polyamory. I most certainly don't want to ruin my marriage. If I had to avoid R, strangling our friendship and trying to forget the way the way that I feel about her, I would be very deeply hurt. I honestly hope it doesn't come to that, but I fear that it will.
I'm not entirely sure that people are wired to be monogamous. Monogamy seems unnatural to me, despite its ubiquity. I'm not certain why that is.
Pushing R - and my feelings for her - away entirely to save my marriage... It might be difficult not to begin to feel a measure of resentment. I would wonder what I was giving in to exactly. It feels almost as though I have always seen that 2 and 2 make 4, while everyone around me believes not only that 2 and 2 make 5 but that I must continue to crush any doubts that 2 and 2 make 5 for the rest of my life. If you have found a thing that makes you happy in one way, you must push away anything else that may make you happy in the same way. This seems to be what the majority of us are taught, and it simply doesn't sit right with me.
Topics for discussion with my wife.