Hey perv Dev,
One of the most important thing to accomplish in order to set boundaries is to raise your standards, knowing that you deserve quality people and not fear losing the person who crosses the boundaries.
If you fear losing the person who overstepped the boundaries then they will learn that it is ok to do so. They will continue to do it once they become aware of this fact.
You will not fear losing them if you develop a set of standards and hold them no matter what. For example, say you want quality friends that won't bring you down, if you stick to your guns it will become easy to let go of lesser quality people in your life.
In order to keep and maintain this standard you will need high self esteem and an abundance mentality. If you feel like you are not worthy of quality people in your life you will hold onto the people who bring you down because you feel you don't deserve it.
As well, if you lack an abundance mentality you will hold onto the people who bring you down because you fear that the 'good' ones just aren't out there. 'I trust the universe to supply my abundance and prosperity' should be repeated when you decide whether or not to keep someone around.
Check out this article I wrote on keeping boundaries in relationships:
Not Setting Rules and Boundaries: Biggest Dating/Relationship Mistakes Part Three