I want him to like me..! Helpp?

So there is this guy i know and i really like him but he has a girlfriend and they've been going out for 6 months but i saw her flirting with another guy just yesterday and they hardly ever talk. Plus she cheated on him once and they broke up but got back together. And a few weeks ago he asked me if i was going on the theatre field trip so i said i was and i did go..And it was today and we ended up sitting beside each other while watching a play. I really wanted him to flirt or something. but he didn't so i tried to show him that i like him. So i played with his jacket string and i started "braiding" his hair..as a joke..And i leaned in really close to him...he would look down and smile at me every now and then..I tried making it obvious that i liked him...But i don't think he got the hint..and we hung out and talked lot after the play and he stayed really close to me while we sat in the cafeteria..A few times he would look at me and he was leaning in so he could talk to the other people sitting around us. how do i get him to like me? Or get him comfortable enough so he'll flirt?