To tell or not to tell

I broke up with my boyfriend of 5 years this past February because we do not get along as we once used to. I would say that I was the one who changed a lot and we just kept arguing. I had already been considering breaking up with him since the ending of last year around October, but tried to give our relationship a chance in case it was capable of being saved. However, I knew it was over for me already and that I had not loved him anymore. Because that was the case, I started talking to an old crush of mine and have not stopped talking to him since. My ex-boyfriend and I still agreed to be friends, but he still treats me like we're still together. He has asked me before if I was talking to anyone, and I just denied it. Just recently, we decided that it was time that we act like a real broken up couple and that we should have space from one another. We plan on having a one last talk for closure soon. My question is, when this final talk happens, do I tell my ex-boyfriend that I have already moved on and am talking to someone else? Do I tell him the truth that I have been talking to this other guy since before our break up? Or is it already enough that I've broken his heart and should just say goodbye? Will it just be adding unnecessary pain to the heartbreak if I told him about this other guy? What should I do? My ex-boyfriend really is a great guy and has been my best friend before we got together. I just also want him to be able to move on.

I personally would just leave it he doesn't need to know ur talking to someone else after all you are broken up and I wouldn't tell him u were talking to someone else b4 you broke up as that would just hurt him more

i think so too, leave the way things are now. have the talk for final closure and keep it in that category moving on forward for both of you.