How do you tell someone your in love with them?

Long story short, i meet a guy and really started to like him. He got with someone else, and I realized i didnt care because im in love with someone else. My best friend of several years. And i mean, im IN LOVE with him. seriously. It didnt hit me that that was why i hadnt been in a relationship in a long time, or why i didnt really like anyone or want to talk to another guy till the guy i "liked" asked out another girl. He told me to just tell my best freind, which i would love to do. But there's a few problems. I dont want to screw up my freindship with him, were best friends. He tells me everything, even what girls he thinks are "hot" and what not. Then there's the big problem. He has a girl friend, who talks about him and everyone else rudely. And i HATE her for it. The one thing I really want to do, everytime i see him, is to tell him to break up with her, and be with me. Hes been with her for almost two years. but ive heard quite a bit about and from her. How do I tell him that im in love with him with out ruining our friendship?