How do deal with inner guilt?

OK so I am not a cruel person by nature. In fact the exact opposite, I want to help anyone and everyone. However, someone really crossed a line with me and I have had to put some pretty strong boundaries in place that basically chased them away... I feel really guilty about it inside but I mean that person really, REALLY took me for a fool and thought they could just get away with it. But again, it's not in my nature to do that. But at the same time, I don't want to take it back because they hurt me deeply. But at the same time, I don't like the situation as it is currently. But at the same time, it's their doing..... How do you deal with the internal guilt of such a case?!