Don’t know how to feel

Okay little backstory, I’ve been best friends with my i guess best friend lol. And this one night we were texting just joking around and she slips in the conversation, that she had already lost her virginity. I of course didn’t believe her cause we always joke around and we’re barely serious most of the time. And she swore it, and seemed serious. Then she had to go sleep and I also left the conversation alone. I don’t know exactly what I felt, but I think I felt betrayal because we always tell each other everything and I’m always here for her. I don’t feel mad though just sad and betrayal. Especially when this happened four years ago. Am I being too dramatic?