I think that your dream is more about an insecurity about your relationship at this point. It sounds like maybe you guys are in a transitional period and you are in a bit of hurt about what may be happening in your marriage. I think that dreams sometimes alert us to aspects of us that we recognize create anxiety. You may just simply be afraid right now or intimidated by distractions. My encouragement is to simply find ways to reconnect and focus on what brought you guys together in the first place.
Does this dream interpretation hit home for you? If you are conscious of a crisis feeling in your marriage, then it may be close to accurate--but dreams don't come to show us something we already know, but something beyond that to point a Positive way forward for us. The management of JustAnswer encourages second opinions from another expert, if the second opinion is significantly different from the first. My approach relies on a very close reading of EVERY detail of the dream, rather than just a generalized mood, and particularly on seeking out every way that the dream details are DIFFERENT from the dreamer's waking attitudes and familiarity with the subject area referred to in the dream.
Your sex with a stranger could point to a part of your self-development that you are needing to embrace, but keep private -- perhaps because your self-concept of what your marriage means won't allow you that kind of personality development. (I suggest this as a possibility, because the stranger might be an inner figure--a masculine part of yourself that grates against your conscious conviction that only your husband can be your true soul-mate.) Did you SEE yourself having sex with a stranger? even SEE what the stranger looked like? Did he remind you of anyone you've ever known or seen (like a movie star)? It feels to me like your sorrow over giving up your sacred pair-bond is both sincere (both consciously and unconsciously) and MUTUAL It's also true that FACEBOOK enables relative strangers to invade each other's private worlds and can thus threaten the sanctity of the marriage relationship.
So could FACEBOOK be having an impact like that on either you or your husband?
If you will try this site again and answer my questions, I will engage in dialogue with you (at no extra charge) until we have arrived together at an understanding of your dream content that helps you move forward with this material to improve your life, and probably also your marriage.