A marriage is a union, and can sometimes be a way a dream illustrates this union. The union can be between you and your inner self ( a regulation of your outer values with your inner ideals) or perhaps a meeting of minds, ideas, anything that is a bringing together of two things in your life. Think about the words marriage and union and do a bit of brainstorming, thinking also about what is going on in your outer life. Chances are you wil have some idea what things in your life are being 'married'.
Don't worry about thinking this dream is about some sort of desired infidelity. If that were the issue, my instinct is that it would take a different form in your dreams.
I know you asked this question six months ago, but perhaps this is still helpful.