I think both of you are at fault here.
you were in an argument and agreed to break up, just agree to disagree and move on.. its not a big deal.. at your age if you think this is the last time you will break up with someone you are dreaming. its gonna happen a lot more times in your life.
is she going to throw your stuff away and are you gonna threaten to ruin their lives every time??
secondly you both have no business being together if you are going to act like that towards one another in the first place.