From time to time it'll surprise me when I remember that my friend has never had a boyfriend.
What makes you surprised that your friend has never had a boyfriend?
I mean come on, I think she's such a beautiful girl.
While you might be surprised that your attractive friend has remained single, it isn't appropriate to speculate about her romantic life or lack thereof. Your friend might have some sensitive issues that have resulted in her choosing to be single and it would be uncomfortable for her to bring up as an explanation if asked. Instead of thinking about your friend's romantic life, try to treat her normally as not everyone wants to be in a relationship.
Are you saying that I'm a bad friend?
No, not at all. I'm just saying that your friend may have not wanted others to know that she has never had a boyfriend and this gossip could hurt her.