I told my best friend my secret and now she's being sarcastic?

I'm not sure if she is but it kinda hurts me. A few days ago, we argued and I ended up telling that I'd sex and I regretted it and she seemed very surprised. She kept insisting that I should go to hospital to see if I get any kind of disease, I should go to police station and report and I should tell my parents about it. I said no but she kept telling she'd accompany me but finally she agreed to keep quiet about it. Then a week later, we met again in school and she smiled as usual. But then when I talked to her, she said "Oh, it's okay. You're always horny, hahaha." I laughed it off but she never said that before and why she suddenly said that. Then again, when we were talking, she said "Don't you just love to unzip your pants and show your banana?" I felt hurt and I was embarrassed because she said that in front of everyone. We've been best friends for 5 years and now I feel like it's a total waste of time being her friend. What do you think? What should I do?