Your new boundary only feels rude to the people who were enjoying the lack of one.

A limit that arrives late always sounds like an accusation to the people it restricts. They had a version of you with no edges, the edges are inconvenient, and the first reaction is often to call you cold or changed. Their discomfort is not evidence that you did something wrong. More often it is evidence the limit was overdue.

Say it once, plainly, without a long justification attached. Expect a rough week and hold the line anyway. Notice who adjusts without a fight, because that tells you a great deal about them.