Is it OK to ask for a hall pass?

I have been with my girlfriend for four years, and I love her to death and intend to get engaged to her soon. There is no one else id rather be with, we connect, love and understand each other. My only issue, is that she is the only woman i`ve been with sexually, and after we get engaged and married will be the only woman I will experience sexually. She on the other hand has had several partners before me. Would it be inappropriate for me to ask for a hall pass, ladies would you be offended if your man asked permission to sleep with other woman, strictly for sex? Are there any guys on this site who have done this. I ain't willing to break up with her for something as shallow as sex, and I respect her too much to cheat.
Is it OK to ask for a hall pass?
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