I think you should sit your wife down and have a talk with her.
People are wired monogomously and they're taught that thinking of someone else and/or developing feelings for someone outside your relationship should be pushed away, etc. The unfortunate thing is, if that happens for a prolonged period of time it is more likely that the person will cheat.
What you do with those feelings are up to you but IMO the first step is to talk to your wife and see how she feels and maybe discuss polyamory with her. Her reaction might be hurt and confused and she might be totally against the idea. If that is so, for the sake of your marriage, you'll have to avoid R before something happens or it ruins your relationship with your wife.
There is no way that a polyamorous relationship can work if the one partner is up for it and the other one isn't.