What worked for me was figuring out what I wanted from the relationship and was I getting it. I also spent some time looking at how much I was willing to invest in trying to make it work.
After spending some time (10 months to be exact) on this I reached the conclusion that she didn't have anything I wanted anymore and I didn't have anything left to give. For me there was no relationship, no trust and to be honest no love. It was simply time to move on.
What I learned in this process was that it was OK to take care of myself and that I had choices. I could use those choices without guilt because if I wasn't willing to take care of me who would.