You think...and think...and think some more. You talk to your girlfriends, your mom, your sister...everyone besides the person you want to leave. That's because you need to make a rational decision and if you talk to him, it'll get irrational real fast! Not that I never talked to Ex, I told him I was unhappy. I asked him to clean up all of his hoarded garbage. I watched Hoarders: buried alive with the sick feeling that I was seeing my future. I gave him a deadline.
The deadline passed.
While trolling the interwebs I discovered this book: Too Good to Leave, Too Bad to Stay. It was amazing...except for the fact that I saw Ex and I in each and every chapter. Each chapter outlines a couple and their issue. The issue is discussed and how it affects the marriage. Then you are given some questions to answer and then told how different people felt after they either left or stayed when they had this issue in their marriage. I didn't even make it through to the end because every single chapter ended with me likely being happy if I left.
It still took many more months, but it did help me start to make a plan.