I am learning something similar, too. I have a particularly hard time accepting that long term relationships have ups and downs, and I always feel so distressed during a difficult period because in my mind, it'll always be this way, it's a downhill spiral, and it's just going to be terrible from here on out. It's like my mind can't comprehend the fact that things CAN get better. I'm slowly (and painfully) teaching myself to realize that relationships are dynamic, and have normal ebbs and flows. Acceptance of that process will only make it easier.