Who really writes the manuals?

I’ve had a few relationships where I feel like the other person initially presented themselves in a way that they could see I responded favorably to. I believed that was how they would continue to act towards me (attentive, complimentary, responsive to my communications, interested in hearing my thoughts, etc.). But each person eventually dropped or lessened those behaviors, and I was left holding a “manual” that I felt they “wrote” but were no longer “following”! So I guess my question or observation is that I feel like I don’t always author the manual myself; people author my manuals for them by acting a certain way and then acting differently. (I hope I’ve explained this well enough!) Any comments or insights?