Ok, well, she DID tell you. She didn't keep it a secret. She is 2000 miles away. She could have easily not told you. How would you know? So, I would tell her your concerns. Be up front and loving and she should understand. Ask her for some things she could do to help you feel more comfortable about it. Maybe calling you when she is with him and introducing you to him or something. It's up to you. I understand how you could feel threatened here. You are not "off base".
