Help!

So I’ve been recently talking this guy for about 2 months, we haven’t had sex yet or defined what we are. Over the weekend I made the mistake of sleeping with someone. After it happen I immediately felt guilty and asked him to leave. The next day I told the guy I’ve been taking to on what I did. He immediately told me he was done and not to talk to again. I tried to explain to him how awful and how sorry I am. I know I’m in the wrong but I can’t help but think about how we never talked about what we are and what the boundaries. I felt like I told him the truth because I didn’t want to hide anything even though I didn’t owe it to him. Now it just back fired and I don’t know what to think, is this really all just my fault or was there just a miscommunication between us that I just didn’t understand. I really like this guy and wish I could take it back.