How do I tell my guy-friend that I want to be his girlfriend?

Patience is a virtue. He's telling you he's not ready and if you respect him, you should really take that into consideration. Keep up your friendship. It will go a long way and it might be totally worth it! Once he's over his gf, he'll be looking at you in a different way. Don't mess it up by pressuring him! Enjoy your friendship and relax.