Although we usually think of a marriage triangle as a dangerous situation, there is one sense in which a third person could create the right triangle.
Viola Walden tells the story of a newly married couple riding a train on their honeymoon. A silver-haired man leaned across the aisle and asked, "Is there a third party going with you on your honeymoon?" The couple looked at him strangely; then he added, "When Sarah and I were married, we invited Jesus to our marriage. One of the first things we did in our new home was to kneel and ask Jesus to make our marriage a love triangle - Sarah, myself, and Jesus. And all three of us have been in love with each other for all 50 years of our married life."
-Sermons Illustrated July/August 1990