Break up advice?

I'm 17 and my boyfriend and I were together for 3 years. About 3 months ago, he broke up with me and said he just didn't have any feelings for me anymore. I'm heartbroken. He's the sweetest guy ever and I'm still madly in love with this boy. Seeing him everyday kills me and the decisions he's been making worry me. I don't know how to handle myself or my feelings and I just want to feel like I can smile again. Tips?