Why do I feel the need to tell all of the details when it isn't his business anymore?

I am making myself crazy. I feel that I need to tell my ex the details of my life when he asks me a question - or if we are just chatting about things.

I have been separated almost a year, and I have moved along with my life fairly well. But, I am constantly apologizing to him for stuff I have no reason to apologize for! For example, I went sailing last fall with friends. Sometimes I was in the company of other people, and sometimes I was in the company of only one guy. I was separated and the other guy and i hit it off. I didn't want the ex to get hurt so, I said there were other people with us when there weren't. I lied to save his feelings.

And now, it is biting me in the ass. We are still separated, and I am going to LA to meet a few of the people that were not actually sailing during the trip, that I said had been. My marble mouth forgot about my lie. I don't know what to say to him next?

Worse - I don't understand why my mouth has verbal diarrhea as I shouldn't be saying anything about anything at all? My ex was abusive during our marriage. For the sake of our son, I have communications with him regularly. I am still very hurt by him and his cruelty. But now - I am a liar and I don't like it one bit.

Any thoughts?