Breaking an ex's heart

So, after my ex broke up with me in August, I started talking to a friend of mine again who I met 4 or 5 months into my relationship with my boyfriend (at the time). I knew he still liked me and honestly I liked him too so once we started talking again we hit it off almost immediately. A few weeks later I had a new boyfriend. A few weeks after that, my ex realizes he made a huge mistake and can't move on. He says he still loves me and everything that happened in the relationship was his fault and he asks for a second chance. I basically told him I didn't think it was a good idea and I didn't want to go through the same thing again and told him I just liked being friends. He understood but wouldn't drop it. He still misses me and still wants to get back together with me but it's already been over a month that I've been with my new bf and I still haven't told my ex because I'm just one of those people that doesn't like to hurt people's feelings. But the fact that I'm too afraid to go completely public with my relationship (on Facebook or just to my ex) bothers my bf and now I don't know what to do. I also want to go public with it, but hurting my ex is keeping me from doing so. And I don't really wanna hide anything from him. I still care....I just want to show him that I've moved on so he gets the message. But....yeah....Do I suck it up and just tell him already or wait until the moment is right?