Gf wants a MFM threesome

So my gf recently told me how she would want to make a mfm threesome a reality, I didn’t know how to handle her say this, I’m ok with dirty talking about her with other guys and using a dildo to roleplay a threesome, but her suggesting to want to make it happen a reality crushed me and idk how to deal with this or what I should think of her. I feel like my view of her has changed because she would be ok with having a random guy fuck her while in a committed relationship. She told me that it’s ok if she never actually has one but just the thought of her wanting one is what is bugging me and changing my perspective of her and I don’t know what to do. Should I break up with her? Should I give her the threesome? Should I try to make things work with it? Is this something that pretty much every girl secretly wants or is it just something that few girls like my gf want?

LSS: Gf suggested a mfm threesome, changed the way I see her, she’s ok without if it never happens, idk want to do because her suggesting it changed how I see her

Edit: I’m a guy btw, just want a girls perspective on this or a guy if there is any on here, and also why would a girl want a mfm threesome when they’re in a good loving relationship?