My boyfriend told me he feels lonely

Anna

He told me that no matter who he’s with he just always feels distant and alone. He said that he feels like a part of him is missing. I was very upset when he told me because he knows he can tell me anything and be comfortable with me. I asked him if he was going to leave me and he said “I don’t want to but I just wanted to tell you because I didn’t want to lead you on.” I don’t understand anything. I’m sitting in my bed crying because I feel like it’s my fault.