Mistakes without the guilt

Let me start out by saying, I am not usually an unfaithful person but this time, I fell off a bit. I have been talking to this amazing guy that treats me like a queen for about a month. Well, I only see him once a week due to his job. For new years we were supposed to hangout at my house watching Netflix but he didn't ever tell me when to go get him so I was home by myself. My friend invited me to a party at his friends to help finish off the alcohol. I knew they would want to have sex but honestly, I wanted it too.

Later that night I was so drunk that I could barely stand up without falling over. Of course, they were drunk too. We had a threesome and it was absolutely mind blowing but I knew it was wrong. (One of the guys has tried for years to have sex with me). Should I tell the guy I'm talking to or keep it to myself?