Well, the short answer is "weakness". The long answer is that the stress from my dysfunctional marriage, inevitable divorce and lack of healthy coping strategies led to my relapse. My current life sucks, but it's 1000x better than when I was married. Instead of building me up, it tore me down. I'm in a much better place to focus on beating PMO and my current streak has been much easier than past attempts.
When I read your old postings I wondered how you could stay married, especially with that sneaking thing with your brother-in-law. To me it sounded even worse than the sexual cheating. Fighting in a marriage is the worst that can happen. Heads up.