Boundaries are subjective and set by the other person, not you, the point is that the boundaries must be enforced. Sounds like there might be more to this story. Writing a message on a pillow is weird, but it doesn't sound like crossing a boundary per se even if it is your personal thing. Boundaries are no joke, believe me it's MUUUUUUUUUUUCCCCCCHHHHHHHHHHH better to accidentally be too rigid about a boundary then to be too loose about one.