Catholic Guilt

I don't know where to start. I would like to start by saying I hate guilt. Its just sitting in the pit of my stomach aching. But I cant really justify it. I made a mistake, my ex and I have a group of mutual friends. It has been three months since he and I split. I am seeing one of our mutual friends now. He found out. He is irate. I feel horrible. Should I? Do I not deserve to be happy? He broke up with ME damn it. Here's the thing, we were friends (the ex and I) we had finally got to a point where we could hang out together and gatherings of these aforementioned friends. Well Saturday night there was a party, we were both there and I was plastered. It was a few hours into the party and he and I were getting along great. Somehow someway, which I cant remember why, I TOLD HIM. WTF? Why would I do that! I really don't remember what he said, I know he was pissed and told me friends were supposed to be off limits. Then he proceeded to take this guy I'm sorta seeing aside and have a 'talk' with him. I was instantly mortified. It was one of those anchorman moments when he jumps in the bear pit to save his woman "I immediately regret this decision". I cant for the life of me figure out why I decided it would be a good idea to tell him! I understand how he could be upset, truly. I have no reason to hurt him I would never want to hurt him, even though he broke my heart. I want to think that we are both adults and that I should be able to date whomever I chose. I feel badly though for making it an uncomfortable situation for everyone involved. I do feel better after writing. I just wish I could take it back, I'm not sure which part though seeing this guy all together or telling the ex. I like the guy though, I would like to see where it goes. I'm I a horrible person? Ugh