How do i make my ex boyfriend regret dumping me?

wouldn't ask me to be his girlfriend, he joined a frat, trust issues were flying everything. Long story short, he played with my heart so much, never asked me to be his girlfriend when i wasted all year with him trying, I did EVERYTHING for him. Needless to say, end of the year I said either take me seriously or we are ending it. He basically ended it. My heart was broken I felt awful, insecure. It was bad. I did everything for him. So currently I'm home for the summer. I'm wondering, when I go back to school how do I make him notice me? When I walk into that frat party how do i make him regret it? I have been working out, I got a new hair cut. I want to talk to other guys but I heard jealousy only goes so far. How do I talk to guys to not look like a and make him mad but make him crazy and completely regret dumping me? SOMEONE HELP PLEASE!