Should I contact my ex?

No! you cut it off for a reason, let him go and then he can know it is over, contact will give hope and yes start the cycle over again. I was in that cycle almost 13 years. if you ever cared you need to ignore him so he and you can move on this chapter is over, when your reading a book do you read the same chapter over and over? I don't, I continue on to the next chapter. When you both moved on then maybe platonic friends is possible, If there is any doubt then your not ready and from what you said in the question your back and forth so it is not time yet. Best of luck