When we are very reactive to certain people, does it say more about us or them?

This question is sparked by recent questions here and also some of my own issues. I find myself quite sensitive to communications from my Ex and also have issues about my best guy friend’s girlfriend. I know both of these situations trigger wounds in me that I am trying to come to terms with. (Not sure you can totally heal from the deepest wounds.) So I am wondering – when someone sets you off, isn’t it worth looking at your own issues first?