Make dates… and break ‘em
Keep asking her out, but let her know you’re not seriously asking her out. All the time. New movie? Bumped into her in the hallway? Ask her out.
“Hey, you know what? I’ve already booked two tickets for that mushy movie that’s out next Friday. You and me, okay? Can you lie to your guy that you have to be with a sick friend and go out with me? Come on… Friday night, okay…!” Or a new restaurant. It doesn’t matter which place, just ask her out all the time, and always just before you’re going to walk out.
It makes her wonder if there’s actually a date on, or not. But you know what? Don’t remind her again. She may actually hesitate to go out with you if you ask, so instead, let her wish she could have gone out with you! If you want to get a girl with a boyfriend, you have to make her want you without ever telling her the truth.