Hi there,
I’m going to offer a different perspective, take it or leave it.
I have spent a large portion of my career working with people who have committed domestic violence, sexual abuse, affairs, and have been caught up in addiction. I can tell you with confidence that if we put aside psychopaths and sadists, everyone else in those categories does not set out with the intention to harm someone else. And yet they do. Someone with pedophilia may love children and believe that they have a loving, mutual relationship with a young person when they are sexual with them, but that does not mean the act is not abusive. It is intentional and it causes harm.
I know that’s an inflammatory comparison, and may make people hate me, but I do that to show that it’s not about how we rationalize things in our minds, and it’s not about people being “good" or “bad" that qualifies something as abuse. It’s about an intentional act that causes harm. Stepping outside of agreed-upon relationship boundaries without being honest and therefore lying to and gaslighting your partner is an intentional act that causes harm. It’s a form of abuse. In order for healing to take place, there should be accountability for these actions. Not excuses or minimizing. In addition to that, as you say, if both parties want to fully heal (whether they stay together or not) they need to do the deeper work of unwinding the roles they played in what got them to that place. Both are true.
I’m certain I’ll get a host of angry comments here, but this comes from a place of knowing that accountability is something deeply lacking in our society and it’s an important part of the deep healing work that must take place. Good people make bad choices and sometimes it can really harm others. It’s important for the healing of all parties to acknowledge that as part of the complex and deep healing work that eventually can affect positive change.