I want to try to answer your question in the sense that you want to tell her, as you ultimately seek a transparent relationship. You find enough warnings in the other Posts so I hope you consider these also!

I can tell you that I currently live in a relationship where it is possible to tell each other such things, but it took time (years!) to get there.

So the first thing you should realize that is that jealousy may play a role wether you have sexual motives or not. I fact, your shared interests of D&D and Programming and the fact that you *really clicked* may be a bigger source of jealousy than even a profound sexual fantasy with an unrelated person (like a movie star). This is especially if she feels she does not share so much of your interests.

You´ll have to build up to that level of trust where it is easy to tell such things to one another. If you have to ask how, you are not there yet. Start small: Does she know when you find another woman attractive and is she okay with it? Or do you still play: *Honey you are the only woman I see!*
Did you share (sexual) fantasies? 

If you feel comfortable with those two topics, then is the time to talk about your dreams. Then, its only about timing and honesty. Bring it up when she is relaxed, obviously. Tell her straightforward. Don´t try to play it down if you feel this is something big. Rather explore together with her what it means. If you know each other this well, you won´t be able to fake it anyway and only raise suspicion. 

At last: little jealousy is ok now and then - if you are both open about it and respect each other! Jealousy is also a sign of affection, and feeling the affection of your partner keeps you relationship fresh.