Yeah, I know what you mean. Often, it is just the suddenness of the change in attitude that is annoying. To go from trusted ally to being at war with the snap of a finger doesn't seem right.

In my HRE campaign, I had kind of the opposite problem with the Moors. They'd attack me and a few turns later ask for peace. Then a few years later they'd attack me again and then again ask for peace a few turns later. I must have fought about ten "wars" with the Moors.