Unplanned pregnancy

How to tell my boyfriend I'm 4 weeks pregnant? We don't live together and I'm afraid he will leave me :( idk what to do. Anyone been in this situation? I'm so stressed and scared. I don't want him to leave me. I'm afraid he is going to because he will be too concerned about what others will think and we aren't married. Any help and support, I'm so nervous scared and alone. I've told my best friend and that is it. It was confirmed at the doctor today. My estimated due date is June 15