Getting a guy from another girl?

Well, this guy let's call him Joe. I like him alot like really really really alot. Let's start from the beginning. When I met him I was just like in love. Something clicked with us. We got really close flirted all the time joked about making out and stuff. And all of a sudden he acted weird. So apparently four days before hanging our his ex and him got back together. I was heart broken have never felt so down before. I still like him and one say he told me really really liked me at one point and I missed my chance. How can I get him back???? Please help!!! Thanks(: