I don’t want to be engaged anymore...help

Hi ladies! So I know this whole story may be crazy but bare with me. I moved out of my parents house in July due to too much fighting and controlling problems, I moved in with a boy I’ve known for 5 years and his father, shortly after that we started seriously dating and he proposed VERY quickly. I was in the moment so of course I said yes and have been bragging about being engaged etc.. well I’ve come to realize this is not truly what i want. I’m 18 and don’t want to be settled this early in my life. I want to move back to my sisters house and be a single lady but I don’t know how to go about that, I don’t know how to tell him I don’t want to marry him and I don’t even want to live here anymore. He’s totally infatuated with me so I hate to break his heart 🙁