It might be futile to try to build platonic, I have experienced severe problems with keeping platonic even if it was clear to me that it wasn't a good relationship, the only way to escape when I was so desperately seeking love and attracted to him so much was to break all contact and keep reminding myself i have to not return to the person, but at that point Original Poster must be self-assured its not a healthy relationship and he is not actually going to change even if he tries to, and that she owes him nothing. Which for me was nearly impossible to do without knowledge and outside help, but also real proof he was cheating on me which i wasn't able to get myself, but my friend did.
In your case and as for most people, platonic doesn't work. Usually the break up has to be mutual, or the emotions have to be in a way that people can eventually accept things as they may turn out. It is not likely, but possible.
I am personally very platonic with an ex whom chose to break up with me. Of course, I will always miss some of those pleasant, steamy moments, but looking back, communication between both of us definitely should've been better and trust on my part. Even though it's not totally my fault with the trust thing because of how I was raised, it doesn't make it much easier to lose such potential quality.