If you and your ex/boyfriend, brake up but you got to attached, but he seems he doesnt want you.. what should you do?

i just need advice, i know " there's alot of guys out there " but he made me change my ways and be different, be my self, for once i though i had someone to keep me up while i was depressed. Until like 2 weeks ago he said he didn't want to be with me and that he just wanted to be single, which isn't what i had in mind. He started acting differently around me, he would always smile ear to ear when he would see me and now we would just mean mug. It's my fault , i opened so much to him and got attached, but i just want your opinions.. what can i do?