<human>: Can you condense the text into three sentences or less?

We've been dating over a year. I had some intimate experience before her with other girls, and she wasn't my first love, but we both lost our virginity to each other. We're both certain we want to marry each other. We never fight, for most of the year we're in a long distance relationship, it works beautifully, and I could never imagine myself loving another. She feels the same. She's the perfect girl- but that's the problem. 

I feel like I can't appreciate her fully because I only ever have sex with her. Imagine if you spent your whole life driving Ferrari's... you wouldn't really be able to appreciate them until you drove something else to compare it to. My girlfriend has told me before that she gets turned on by the idea of me dancing with other girls in the club, but then going home with her, being hers at the end of the night. She likes the idea of me being "hers" at the end of the day. And I love being hers. 

She's my whole life, and I could never leave her. I don't want anything emotional with other girls- just NSA sex, maybe even less. I want to experience other girls so I don't resent her later on in life for robbing me of experience. Leaving her is not an option. I'm not sure if she'd be up for a threesome, and I'm hesitant to ask, even though we're very open about our sexual preferences. Would asking for a one-sided open relationship be completely ridiculous? Leaving her in any way is out of the question. Thank ya'll for your advice

Obligatory "Sorry for rambling" comment..
<bot>: She's my whole life, and we intend to marry. But I want to experience other girls so I can appreciate her fully, instead of resent her. Advice?