Help! Does she like me? I hope not!

I have been in a relationship with my girlfriend for 9 months, we are at university and I love her to bits. She does too. We have a common friend whom we both get along really well with. However, I talk to her quite a bit on Facebook and in person. We have a lot in common and have similar tastes(something which my girlfriend and I also share). Now, this friend of ours has been talking to me a bit 'extra' on Facebook over the past few days, even asking me if I'd like to go with her to this event she was going to. Today, we spoke on Facebook for over 2 hours and were talking about everything under the sun, and having so much fun. Towards the end of the conversation, she said 'Ok I'm going to say something really corny. When I speak to you, I feel like I'm speaking to a long-lost twin. You think eerily like me'. That was a bit funny. And weird according to me. We also speak about my girlfriend and I told her how much I loved her. I'm just a bit confused. Am I overreacting unnecessarily?

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