How old are you exactly? could help in the process.
options: confront her head on, maybe she's trying to make you jealous by hanging around him waiting for you to man up playing one of those evil games women always play.
option 2: step back, meditate, invest in bulk, get a hobby, finish reborn, run a marathon, do some shopping, take a singing class, experiment with boys have a party, do some soul searching. There's so much to do with your life at a young age.