This material is a bit dry, but for anyone accepting blame due to cheating it's probably worth skimming through: https://www.amazon.com/gp/product/1572303670
It's about the anatomy of bad relationships, how each party feels and acts, including the triangle aspect. How events play out and why.
It can be a big relief to recognize that we have played out an incredibly common pattern, when our culture is sending us all these hopelessly unrealistic superficial messages that we're failures, betrayers, at fault, guilty, whatever else.