My friend I've had for 8 years said she can't come over, but my best friend is over her house?

My best friend, Katie, just told me she was going to go over Taylor's house Saturday through Sunday. Taylor and I have been friends since we were 4, and I am now 12! So anyways, I really wanted to hang out with Taylor this weekend so I asked her to come over. But, she said she had a family thing over the weekend so she couldn't. But now, Katie IMs me and tells me that Taylor just invited her over. I immediately got jealous. Not by choice. It's just that everyone loves Katie. She is just absolutely perfect. So now the person I have been friends with for 8 years can't hang out but is hanging out with a person she's known for a month?