More people in a relationship introduces a larger surface area for interpersonal conflict. Communication is always hard even for two people, not to mention jeal

More people in a relationship introduces a larger surface area for interpersonal conflict. Communication is always hard even for two people, not to mention jealousy and the challenge of learning to live with another. It becomes exponentially harder when a third person is added. That just adds to the chances of instability between parents. 2 parents is essentially a stable maximum