Having been in a triad relationship for a little more than five years now I can honestly say that it is one of the most difficult, yet amazingly rewarding experiences, I have ever set upon. If you and your wife have another that you both want to be a part of your relationship I say with enthusiasm - Hang in there! It's all about the commitment.
Upon reaching the point at which jealousy retreats and honesty and love come together, speaking from my experience, there is not a monogamous relationship that can compete.
I wish you wellness and happiness in your journeys.