I think we are often at risk for making expedient, self-serving decisions. Polyamory is not a magic bullet that suddenly makes me transparent, 100% consistently ethical, honest, willing to face pain to stay in integrity, etc.
I lived for many years in a wide variety of profound self-delusions. One of those was "this relationship is broken, I need a new one. " Another: "I will get it right this time. I will be a better person and get it right." Another: "Those other women were just not The One. This one now is The One (or: the NEXT one will be The One)." Etc. Serial monogamy was as much of a recipe for self-deceit as non-monogamy or poly is for me. The key thing for me is to pray, meditate, communicate, communicate, communicate. And not just with people in the relationships either, but with many friends, with community, with advisers who are trusted, etc.