If you think other issues are causing significant dissatisfaction in your relationship, I'd tell your wife you don't want to lose focus on those things, that you want to try to work on these things while you learn about and consider opening your marriage.
Early this year 2012 , she approached me and told me that she had feelings for a male coworker and that she needed to tell me about it.
Honestly it would be better if she came right up to you and said monogamy isn't for me anymore.
I can see some parallels between your situation and mine, except that it is flipped.
We are still researching this one.
After figuring out how to discuss your open relationship with each other, you should agree on how to talk about it with others, if at all.