There's no known magic words for this kind of a conversation. You just have to talk to your wife, with an emphasis on being very honest and candid about your feelings, and sensitive and respectful toward her feelings. There's no guarantee she'll consent happily or even at all. It's her right and privilege to be the one who decides what she herself is or isn't okay with.
I would recommend having a "Plan B" in mind for if she says "No." Is that a dealbreaker for you, or is staying with your wife more important to you than exploring these poly inclinations you've been experiencing? Can you be monogamous for her? Do you want to?
You might have to have more than one discussion with her to arrive at a certainty about how she feels. It sounds like there's a chance she'll say "Yes" just because she wants to tell you what you want to hear. But you need to hear the truth. Maybe you'll even proceed to see other women, but if you do take it slow and check in with your wife often.
Love means never having to say, "Put down that meat cleaver!"