Most Helpful Guy
Breakups, in general, are difficult. Breaking up while continuing a friendship with an ex is insurmountable to many.
Remaining friends and regularly interacting with an ex whom you attached and feelings for is not conducive to recovering from the breakup in the most effective, least painful manner. The exception, perhaps, would be if you lived hundreds or thousands of miles apart from each other.
In any event, sisters and bothers you are not, in any context, so do yourself a service by not referring to him as such, and, by all means, do not address him as such. You have a fairly recent emotional, romantic history with him. He is presently not, and perhaps may never will be, just your friend.
Having said that, I strongly encourage you to distance yourself from him as much as your circumstances allow. Limit your interactions with him to unavoidable situations; for example, avoid conversing with him on Facebook, school, or mutual friends, etc., whenever possible. In other words, give yourself the necessary time to accept the breakup, to mourn, and completely heal.
If you must, I suggest revisiting being friends with him after your feelings for him are no longer romantic. Otherwise, your pain, in it's present form, may be constant and resisting for indefinite period.