Sandi, this is such a great thread. I agree, there is a gray area in terms of responsibility for unhappiness. Ultimately, we are each responsible for our own happiness, but in a MR we each have needs/wants that our S should at least try to fulfill. My H had an affair. I am not responsible for his decision to enter into the A. I am responsible for neglecting his needs in the M prior to that. I am not fully responsible for the breakdown of the M though. We both own a portion.
It seems like most breakdowns start from having too many expectations of the other person, thinking all of our needs should be fulfilled within the MR, and not appreciating the efforts the S does put forth. I know in my case, prior to the A, we were both angry about what the other person wasn't doing. But neither one of us was clear about what we expected or needed. Now we are clear. We also tell each other what we do appreciate and are generally much kinder to one another.
Me: 30 H: 35 M: 5 years S2 Signs of MLC started Feb 2014 BD - PA July 2014 Piecing/reconciling late July 2014