The pain that you caused was deep, and it hurt because it mattered. When someone does something to you it does not cause pain unless you care. If someone that you do not know wrongs you or says harsh things about you it is irrelevant and does not have an impact. If the other person does not matter then neither do their words or actions. When someone is close to you they have the ability to wound deeply though, sometimes without ever meaning to. If you find out your beloved has another or your spouse is having an affair this can be extremely painful because it matters and it affects you on a very deep level. If the neighbor down the street is cheating it does not have the same impact.
In any relationship your words and actions can have an enormous impact on others. Take care to think before you speak or act so that you do not hurt those that you care about the most. When you love someone you care what they think, and you want them to be loyal and committed. When they are negative in their words or they act in a way that makes you think they don't care it matters very much and it can hurt more than a physical wound. If someone makes a habit out of hurting you then it may be time to rethink the entire relationship because you deserve better, someone who will put you first and make every attempt to make you happy instead of causing you pain.