Usually I could trace my obsession to a cause that had NOTHING to do with him. There were hormonal shifts, or my self-esteem had just taken a kick to the shins for some reason, or I wasn't feel good about myself, or I wasn't getting enough sleep, or or or or, and just like picking at a scab, my mind went back to him. My favorite obsession target.

Years of habit have burned neat little neural pathways between certain feelings and your ex. You're still in the process of rewiring them. Ride these waves out as best you can and try to do better each time they hit you.