<human>: I've been with this girl for less than a month, and things have been going very well. I feel very fortunate to be with such a beautiful and ambitious person. I'm open and honest with her and want to communicate as much as possible; which brings me to the title of this post.

I must stress how short our relationship has been at this point. It hasn't been long at all, and I feel I may be overreacting to a small situation.

We (mostly I) made plans to go rock-climbing. She texted me recently saying how she would like to do it later, and she wants to have dinner with her friend (female.. but it doesn't matter) instead. I wrote her back saying, "okay, have fun".

On the inside, I felt like we had plans to do something together, and I was very excited. Now that the plans are gone, I feel perturbed. Should I tell her how I feel, or should I go on pretending I'm completely fine with what happened?

Can you condense the text into a few key points?
<bot>: Girlfriend canceled plans and instead is having dinner with a friend. I'm acting like I'm okay, but I'm slightly upset. Should I let her know how I feel?