David, I could have written your post! I am forever obsessing, tweaking, wondering what would happen if I did (insert random diet and/or exercise change here). I weigh and measure myself too often and compare my progress to others constantly. All bad things.
Here is what I am doing to try to forget about the marshmallow. Now that I understand how the whole PB thing works, I just started a 6-week plan where I have promised myself not to change anything for that 60 days. I won't add or remove foods or workouts, no calorie or ratio counting, no weighing or measuring. I will listen to my body and what it needs, and whatever the outcome after 6 weeks is what it is. I'm doing healthy things for my body so I have to let it change at its own pace. It ain't gonna be easy, but I really need to get out of my obsessive rut!