This may mean that you need to do something special, incredible, unique and impressive that would make the guy consider you alone than the other girl. This could be your behavior, your personality and the way you handle yourself.
No, no, no. Play your cards right? Give me a break!! First of all, the guy is CHEATING on his girlfriend. If he'll cheat on her, he'll cheat on you too. Sorry, but he's messing with your head & trying to get you to compete for him. You deserve better. Don't sell yourself short on this loser!! Move on to somebody who chases YOU.