Can I be honest?

So I feel like I’m currently having this internal battle with myself, one minute I’m thinking about me (26M) and my gf (26F)together in a strictly monogamous relationship where we don’t share each other and whatnot, and we are only for one another. However, she has expressed to me that she fantasizes about having a threesome with another woman and how she very sexually attracted to women, but not romantically, and although I have talked to her about it and have tried to get her to understand that it might not be the best thing to do, considering the fact that she’s just like me where she’s super possessive and all about me, at the same time I can’t help but to think about how hot it is for another girl to be involved with us sexually only and for a threesome to happen and all, one minute I’m like no, then the next I want my girlfriend and I to have a threesome with another girl, or if the opportunity arose even an orgy, I often fantasize about group scenarios with us involved, or at the very least us not necessarily involved with anyone but one another, but just being in the same space of it happening. I think one of my biggest fantasies/kinks is some sort of exhibitionism or voyuerism to a certain degree, I just need help navigating my feelings and what we should do!