Why is my friend so jealous of a girl I hang out with?

Alexandria and Bre met a few days ago and alexandria likes Bre`s company so I just don`t understand why Bre get mad when I do things with alexandria and not with her? Me and Bre use to do things together all the time!!!!! But I want to do other things with Alexandria the girl I really like, I`m thinking about asking her out. we always text each other in class, we go off campus for lunch, and we are always together. The problem started yesterday when me and Alexandria was about to leave for lunch, When I got home to check my Myspace bre left me a message that shocked me,all this ugly language and how I left her out in the cold, she is ticked she acts like we have to do everything together and it ticks me off. she starts claiming I left her out in the cold . she can be a hypocrite sometimes and she does`nt want to admit it. we have been friends since freshmen year in high school now I am a senior. Is Bre jealous that I do things with other people? I don`t understand because I was keep in contact with her now she is mad because I spend time with Alexandria. Does she think that my relationship with Alexandria can harm our friendship. Any advise?Why is my friend so jealous of a girl I hang out with?
Sounds like she wants, or thinks you have more than friendship. She also doesn't want to share you with anyone. She is the clinging kind of friend that wants to be included in everything and the center of attention. If you don't think of her as your girlfriend, but just a friend I would tell her that you will be friends with a lot of people and also have the right to go do things with whom ever you please, but that you value her friendship, but won't let her rule your life. Why is my friend so jealous of a girl I hang out with?
It is your mistake that you kept her so close one time and now you are pushing her away..............you made her trust you and felt comfortable around you..........Stop acting so quickly but you can try to keep her but loosening the grips day by day. This might act like a simple solution.
Dude she likes you, and is jealous. Hey tell her this. Say I like you and that girls is just someone I hang out with, tell her you have no feelings for Bre. Not that hard