It's more than a little bewildering, isn't it? Here we are, ready to make that final commitment to the man who won our heart, ready to publicly wear our vows of fidelity and honor for the whole world to see (should they look to our ring finger), ready to have and to hold "'til death do us part," and suddenly we begin dreaming of having sex with his brother? And an ex-lover? And more than once or twice. . .as in a lot?
If you're wondering what is up with this dream, you're not alone -- which I hope makes you feel better. The truth is, dreams of old loves, of exes, of the guy at the sandwich shop, of the cute bank teller who drives the nice car, all surge just as we stand on the brink of this very major commitment. Women begin dreaming of guys they haven't seen or thought of in ten years. Guys start flipping through the Rolodex in their minds at a frantic pace. It may not be right, but it is natural. What causes it? Is it a "missed opportunity" syndrome? Or is it, as you suggest, nerves?
The context of your dreams gives us the biggest clue as to their meaning. While it most likely is true that you find your husband's brother attractive (and we know that, at one time, you found your ex attractive), the timing of the dreams -- arriving as they did on the eve of your wedding -- suggests a motivation other than smoldering sexual desire.
Because marriage is unknown territory for those not yet initiated, it is natural that we fear it a bit. One of our greatest fears, which frequently masquerades as "doubts about our partner," is self-doubt concerning our ability to participate in the relationship as we have promised. In the shadow of this fear, your dreams show both a desire to return to the safety of a known relationship (your ex), and also a desire to sabotage your relationship with your husband -- so you won't have to face your fears -- by having a relationship with his brother.
To answer your questions specifically: Do you really want a relationship with your husband's brother, or with your ex? The answer to both questions almost certainly is a resounding "No." What you really want, thankfully, is what you have.
I'm glad you stuck out those nervous days (despite your dreams), and held on to the man you truly love. Congratulations on your marriage. I wish you the best of luck as you set out to build your family.