Advice on what? You did the right thing by breaking up with him. He was your ex so I'm not sure how you managed to break up with someone you weren't even committed to but that's neither here nor there. Point is, that you want to pursue other guys, your ex is an ex because you barely saw one another and right now you're just confused.
stop all contact with your ex once and for all and get on with letting that guy at school know, through your actions that you are interested in him.
You'll be fine, just keep busy, do lots of fun things with your friends and family so that your mind is off him and in no time at all, you'll find you no longer are missing him.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion