You are attracted to guys. Where do you think this penis is going to come from if not attached to a guy?
Nobody is saying you have to
fall in love with a guy, but you are curious enough and sexually attracted enough to want to try it. That means you being "straight" no longer applies for the moment. Your orientation is officially "bi-curious." That alone is probably a big deal to your fiancée, and she probably never imagined that before so it could take a while for her to figure that out.
By the way I really like your reasons for
wanting to try it:
I just wanna see how things are from like her prospective while she's doing stiff yo me... I wanna no what it's like to stroke suck and ride a cock!
I think that is erotic and hot, and also I like the fact that you want to explore sensations from her point of view. I agree that it could bring you together with a shared experience instead of driving you apart. I believe you, you're just looking for something fun in bed, to learn about and try something new and it could teach you as much about
her experience as your own or the other guy's.
But you know this is experimental and unusual as far as relationships go, right? Not many people have even thought of an idea like this. Even fewer people know how to make it work. It is natural that she would need a lot of time to even understand how this would work, before she even thinks about whether she wants to or not.
The bottom line is, I have no idea what she believes or why. Have you asked her? It is a big deal that you don't agree on this. You need to let her know that this curiosity is real, and sincere, and part of you. Let her know that you don't have to act on it, and you love being with her, but that every time she's fucking you she's fucking a man who is also curious about getting fucked, and that isn't going to change.
She may be interested in monogamy only. Most people are. And this may be a deal-breaker for her. One more thing, when you talk about it with her, let her try to convince you too. If you want her to change her mind, you have to be just as willing to change yours.
That is probably the best approach. Give
her a chance to convince
you that it is a bad idea. Once she starts explaining her feelings, she might change her mind. You both might come up with something else that you both find hot. Or she might change
your mind completely. At least you will know what her feelings are.