Personal boundaries are things like you mentioned, but there are also relationship boundaries. You seem to call those rules, I guess some could be called either, but rule to me implies something is wrong. No cheating is a rule. But a boundary moreso to me feels like "I do not feel comfortable going beyond this" For example, if my partner sleeps with someone else without checking in with me, that break a boundary, and it is cheating. If they talk to me first and I am ok with it, it does not cross a boundary. It is no longer cheating. No cheating is a rule, no problem so far. But cheating is relative to our boundaries.