Why is my friend acting like this?

I have been friends with Ryan since we were in third grade. We live close to each other so our moms are friends too. Ryan has also been friends with Jack, another boy in our neighborhood. Jack and I went to preschool together so we know each other, but we have never hung out. Jack went to a different grade school than Ryan and I did. Now we are all together in the same high school and I have Jack in a cl and he plays on a team that I am involved with so we are getting to each other better and becoming friends too. All of a sudden, Ryan is acting like a jerk and I can't figure out why! I asked Ryan for Jack's phone number once because my mom needed to ask Jack's mom if she could pick me up too from a team practice one day and Ryan wouldn't give it to me. He kept saying he was too busy. My mom finally got it somewhere else. The other day, he saw Jack and I talking and he went ballistic, "pretending" to be fighting us. His personality has definitely changed since Jack and I are becoming friends. What is going on? Thanks!