How do you know if a boy likes you?? What can I do to make him like me a lot?

A boy who is a friend of mine, asks me to sit next to him in lessons and when I sit next to him, he touches my leg. I'm starting to like him a lot moe then a friend, but he has got a girlfriend and my best friend fancies him as well, but I don't tell her that I fancy him as well. What can I do to make this boy like me more?