Little Help? (Boys)

Ok,so I am really 11 years old.I am having boy troubles at the moment.My mom says I can date boys my age or one year older,but Alex is 15.He is so* cute though!I really like him alot.Another problem is he has a sister my age,and we're bestfriends.I don't want to tell her I made out with her big brother,but I don't know what to do.Another huge* problem is my older brother he is 17 and hangs out with Alex!My brother dose'nt even let me talk to his friends,let alone date them in secret!I really don't know what to do.I am very happy with him.Even though it is weird.