First, I'll tell you that I understand how you are feeling. I'm a wee bit protective of my men as well. And I don't like for them to be hurt...by me or any one else in their lives (it doesn't have to be a romantic relationship). If I've been the one to hurt them, and I''m realistic enough to face that not only have I done so but I will again, I can make amends for that. We can talk, work on it and sometimes cry about it.
However, if it is someone else that has hurt them, I can't do any of that. I can be there for them, support them, and listen to them. I can not be a part of the healing process in a constructive way.
And it does at times anger me. Particularly when it is a habitual behavior on someone's part. Kitten is often selfish and passive aggressive. It's hurtful. But I've had to accept that my men are adults. They chose what behavior they are willing to accept and live with. While I don't like seeing how they get hurt, accepting this behavior, from Kitten or even anything I dish out, is ultimately their responsibility.
Since they accept more of this type behavior than I am willing to, it was a difficult road for me in getting to this place of sounding board if needed and not trying to fix things.