Thought I was ready to be in a relationship, only to find out I am not. How to break up with him nicely.?

The love of my life broke up with me, breaking my heart about a years and 4 months ago. I have spent that time, trying to get over him and after a year of being broken up started dating again. I meet a man 3 months who sparked my interest and we started dating, and now have been boyfriend/girlfriend for about a month. The thing is, I have come to realize that being in a relationship is causing me heartache and grief. I really like this guy, I am just not ready to be committed to him. How do I break it off nicely with him?