Well, I am pretty new here, so I hope it is ok for me to put my two cents in. I believe that it is always best to find out if someone can accept you for who you are upfront, than to lose them later due to a misunderstanding after much emotional investment has taken place. If a person is not able to accept you for who you are or even (much in my case) understand who you are than there could never be a relationship of any value regardless of if the news strikes early or late.
I would also take carful consideration into talking someone into being honest with their spouse. It may be worthwhile to direct them to new ideas, but convincing them to do something that could put them at a loss could potentially put you in a difficult position.