Right to Worry?

I met my girlfriend on a vacation weekend and found out she still lived with her ex-boyfriend of 3 years. She said she moved into the guest room, which I believe. However, I have not met him, so I am sure he doesn't know of me. I don't feel she is cheating on me or anything, but I can't help but feel like I am part of an affair. The only thing that worries me is, she is still really close to his family and still attends some family functions. Am I paranoid, or do I have the right to worry?

— Nick, 26