Direct Answer: If a partner repeatedly crosses a boundary, the problem is no longer communication; it is a failure of follow-through. A boundary is not a threat to make them stop; it is an action *you* take when they don't. If they ignore your limits, you must immediately execute your stated consequence rather than offering another explanation.
When a boundary is crossed, our default instinct is to explain *why* it hurt us again. We assume that if our partner truly understood our pain, they would stop. However, if you have explained it three times, they already understand. By continuing to explain instead of taking action, you are teaching them that crossing your boundary only costs them a 15-minute conversation. You are reinforcing the crossing.