I think part of getting to that place where you are willing to stop allowing others to tread on you and dictate how you can be have in a relationship, is that you have to recognize that YOU are a big part of that problem.
If you can honestly recognize that YOU are allowing someone to do this to you, that YOU aren't valuing yourself...THEN you are more likely to make the changes necessary to stop being a doormat. Unfortunately taking that close of a look at yourself is often really painful, it hurts to know that you are directly responsible for a great deal of the pain you endure....even though the other person is dishing it out. It REALLY hurts to know that not only does the other person not value you the way you want them to, but neither do you.
For me, when I recognized that I got downright pissed off at myself...and that's when I began to really step up. That's when I realized "what have I got to lose?
