Please help.. HOw do i get my ex back?

my ex bofriend jus broke up wit my exactly last tuesday for no reason. he said that it was cause we are both 2 different ppl and we shouldnt see each other anymore. i mean he has been actin so weird for 2 weeks before that too. ever since the prom after party. and that night his ex was making out wit like 5 guys and he had seen it. i guess it hurt him or something, because maybe he still had feeling for her. well ever since then he hasnt been the same person towards me and jus last week he broke up wit me. then jus this saturday i found out from his friend that he wants his ex back. so was it because those kisses made him jealous? and i really liek him i jus want him back? how could i do that. make him jealous? not talk to him for a while? i don t know.. please help me.