My crush ignores me after he used to flirt with me everyday!

Ok, so theres this boy I like..he's in some of my classes but the only one we really talk in is English. our desks are in rows and he sits in my row. There's 4 desks and the seats go, him, a kid, me, then a empty seat. Everyday he goes back and sits in the desk behind me because "he likes leaning against the wall". Almost everyday he likes to poke and squeeze my sides while we're sitting their cause he knows I'm super ticklish. He always shoulder checks me and when we are sitting in English he also likes to play with my hood when I have a hoodie on and he always plays with my hair. One day in English me and my bestfriend got into a little argument over something stupid and she was just sitting there crying and so was I and he kept telling me to go talk to her and I don't know he was just like comforting me. Also I'll be walking behind him and he just stops real fast and ticks out his butt so I run into it. Well to get to the point, him and this girl (that I don't like) started dating two days ago. Yesterday in English he didn't sit behind me, he sat on the way other side of the room with his friend. He didn't talk to me at all. Also today he sat in the same spot and again didn't talk to me at all. we make eye contact a few times but he just looks away..my question is: why is he ignoring me since he got a girlfriend? And I really really like him but I don't wanna be a b**ch and break him and her up just so I can get him. I mean I want him to be happy. I just really miss him already lol :/ I don't know what to doooooooo! :/