No closure

How do you get over a breakup if there was no closure? This break up happened for no reason. And my now ex is saying it’s because someone else gave me a hickey but the hickey came from him and I have not been unfaithful in any way shape or form during our relationship. I don’t know how to deal with this heartbreak since I don’t even know why its happening. He obviously gave me the hickey as no one has been that close to me but him, but he doesn’t remember it and it caused our relationship to end when there was nothing wrong with our relationship. We never had any problems. And i truly loved him so much. I don’t know what to do