Maintaining healthy boundaries takes two. You lay down your boundary, but the other person has to respect it. When they won’t respect you, that’s when you have to either let them cross your boundary or stop them in their tracks by getting away from them (literally physically leaving or ending the relationship).
There’s pain in ending those relationships. It may be with a person who you thought cares about you. But if they don’t have any respect for you, do it they really care for you? There’s grieving when you enforce your boundary and end the relationship, even when it was an abusive one.